Greetings, PRIVATES, my name is FIELD GENERAL PIPSQUEAK. I'm here to tell you all the useful information that STUPID ROBOT at the training centre neglected to tell you.
This is by no means a comprehensive guide, simply a collection of useful pieces of information that can make the difference between you getting on that EXTRACTION SHUTTLE alive and ending up a smear on some HULK's shield. This means knowing the faction that you are currently bringing MANAGED DEMOCRACY to with HEAVY ORDNANCE, the best weapons to use while doing so, and advice on using STRATAGEMS properly.

By far the most common sight in the galaxy, and the one which you'll likely go into battle with first. Do not underestimate the bugs, while they may be stupid, they are heavily armoured. Be prepared to face swarms of hostiles that are able to shrug off most gunfire.

By far the best weapon to use fighting BUGS is the AR-20L JUSTICE. However this is locked to rank 18, so you'll have to make do with the AR-19 LIBERATOR instead. Aim for centre of mass and your rounds should penetrate fine.
The most important lesson to learn when fighting BUGS is not to panic. When wounded, WARRIORS will charge at you in the hopes of you responding with fully-automatic fire. Such a response will only empty your magazine and waste precious rounds. Remember your training and fire in controlled bursts to penetrate its armour and bring it down.
If you have it, the AP-AMMO and SLOWING ammunition of the AR-14D PARAGON is a worthy substitute for the AR-20L at low ranks. The SLOWING effect is particularly useful for halting charging WARRIORS.
Laser weapons such as the LAS-5 SCYTHE and the LAS-16 SICKLE are also useful when fighting BUGS as their precision allows you to accurately target weak-points. These are always bright orange, by the way. The exception is the LAS-13 TRIDENT, which is suboptimal because of its inaccuracy.
For the aspiring marksman, the M2016 CONSTITUTION makes a good weapon against BUGS, as it's high damage and AP-AMMO make punching through armour easy. However it's of limited use against SCOUTS, and you may find yourself swarmed by too many hostiles for the weapon to handle.
Be aware the M2016 reloads rounds one at a time.

For secondary weapons, the MG-94 MACHINE GUN is not a good choice against BUGS due to it's innacuracy. You will often finding yourself burning through ammo as you struggle to hit centre mass. The LAS-98 is a much better choice, not only is it pinpoint accurate but it also allows you to move while aiming without upgrades. Perfect for the aspiring bug-hunter.
The FLAM-40 INCINERATOR can sometimes be useful, although it may take a while for an enemy to burn to death. I shouldn't have to tell you to be careful while using this weapon, though if you are careless enough to catch fire diving to prone will extinguish you. The FLAM-40 can ignite heavily armoured hostiles, though you will need to hit their weak-point to do so.
The RL-112 RECOILLESS RIFLE and the EAT-17 EXPENDABLE ANTI-TANK WEAPON are your best friends while fighting larger BUGS. The RL-112, when fully upgraded, will take out ANY standard enemy you encounter in a single round. If you require two, or there is more than one TANK bearing down on you, the SUPPORT BACK included in the HELLPOD reloads the weapon.
Be warned, it takes a significant amount of time to reload a RL-112 on your own. Having a fellow HELLDIVER pick up the support pack cuts the reload time from 5 agonizing seconds to less than one. Having a teammate can be very helpful when facing multiple TANKS, though only if they manage to stay alive as well.
The EAT-17 is a one-shot weapon, but each HELLPOD always contains two. Either call it down when you need it and take the spare along afterwards, or call it down early and have two HELLDIVERS take one each. Be warned, the EAT-17 has a cooldown time of 2 minutes.

As a final note, the RL-112 and EAT-17 can be used to destroy BUG NESTS, which saves you the hassle of waiting for a HELLBOMB.

Unlike BUGS, CYBORG scout teams contain one SQUADLEADER with a grenade launcher arm and two to three INITIATES. Always aim for the SQUADLEADER first, as they are the only ones capable of sounding an ALARM and are much more dangerous in combat.

Counterintuitively, the CYBORGS have fewer armoured units than the BUGS, though they are significantly more dangerous. The AR-19 LIBERATOR is the best weapon to use here, although the increased damage of the AR-20L JUSTICE can be useful in killing squad leaders. The difficulty is often not in penetrating a CYBORG's armour, but in filling it with enough lead that the damnable thing actually dies.
Shotguns like the SG-225 BREAKER and the SG-8 PUNISHER are highly useful for taking out CYBORG patrols as well a fending off CYBER HOUNDS, which will attempt to surround and incapacitate a single HELLDIVER. Always remember that weapons fire will pass over allies when they are DOWNED.
The CR-9 SUPPRESSOR is a useful weapon to use against SQUADLEADERS, if you have access to it. It's explosive rounds can often destroy a patrol before it has the chance to sound the alarm, though watch your ammunition consumption.

The MG-94 MACHINE GUN comes into it's own on CYBORG controlled planets, useful for mowing down both patrols and attacking hostiles. Be sure to upgrade it to allow for firing while on the move.
The RL-112 RECOILLESS RIFLE and EAT-17 EXPENDABLE ANTI-TANK WEAPON are still as useful as ever, although unlike TANKs, the weakspot on HULKs is the belly. Make sure you do not hit a HULK's shield, as it is completely immune to anti-tank fire.

If there are CYBORG AA EMPLACEMENTS present on the map, be sure to take along a RL-112 or a few EAT-17s to deal with them. They are always protected by a JAMMING FIELD which will block all stratagem use. You can disable it, but it is generally faster to hit the AA guns with rockets.

Absolute flower-sniffing, tree-hugging, animal-not-eating, armour-not-wearing, limp-wristed, squid-brained PANSIES. Forget armour-piercing ammunition and anti-tank weapons, what you need here is GUNFIRE. And lots of it!
ILLUMINATE scouts are only a single unit, the cloaked OBSERVER. This unit will falter under even pistol fire, and it's much vaunted cloak is clearly visible due to the light it's scanning eye gives off. It is also very visible when sounding the alarm, as it will open up and spin.

Possibly the only enemy which merits the use of the AR-22C Patriot, though watch your ammunition consumption as you will not have the luxury of sitting still to wait for a HELLPOD.
Be careful when taking short range weapons like shotguns or submachineguns, as HUNTERs and OBELISKs often fire their weapons from outside visual range and countering these enemies is crucial to maintaining battlefield mobility and protecting OBJECTIVES.
The main considerations when choosing weapons are TRIPODs and OBELISKs. The latter is a moderately armoured close-combat unit. treat them like BUG WARRIORS and you will do fine. OBELISKS are much harder to counter, as their heavy armour makes them invulnerable to all but the heaviest anti-tank weapons. They will drop the armour to attack, giving you a few precious seconds to kill them.
ILLUMINATE shields will block UNSTOPPABLE rounds, making the RX-1 RAIL GUN and to a lesser extent the AR-20L JUSTICE less effective. Avoid taking these weapons.

The OBLITERATOR GRENADE LAUNCHER and the MLS-4X COMMANDO are highly useful, as they are indirect fire weapons capable of firing over OBELISK shield-walls. The HOMING rockets of the MLS-4X are particularly useful for reliably killing hostiles beyond visual range.
The best weapons when fighting ILLUMINATE forces are often STRATAGEMS, especially low-cooldown ones. The STRAFING RUN is an excellent choice, capable of killing most ILLUMIATE forces even at high difficulties. Beacons can also be thrown over OBELISK shield-walls.

OBELISKs will often be the most difficult part of a mission in ILLUMINATE-controlled space. Their shield-walls can quickly isolate HELLDIVERS for the TRIPODS to hunt down one-by-one, and will block movement and weapons fire. However, they have a crucial weakness...
While deadly when moving, if a HELLDIVER stands still as an OBELISK projects it's shield-wall it will cut the wall short without harming the HELLDIVER. The best defence when spotting the rapid flashing that heralds a shield-wall is often to stand still, as you will have greater mobility by cutting a shield-wall short.
Learn the difference between HUNTER energy beams and OBELISK shield-walls. It may give you the crucial edge you need.

Avoid the MG-105 STALWART. It suffers from the same accuracy problems as the MG-94 and has a smaller magazine. If the job would be done adequately by the MG-105, it can always be done better by the MG-94.

SMGs not only allow a HELLDIVER to move faster, but can be used one-handed. This makes them perfect for those carrying a BLACK BOX or ILLUMINATE POWER CORE to keep up with their teammates while still being able to adequately defend themselves. The extra speed can also help a HELLDIVER using an anti-tank weapon get into position for a kill-shot.

There are multiple solutions for destroying objectives without calling in a HELLBOMB.
EAT-17 EXPENDABLE ANTI-TANK WEAPON
REC-6 DEMOLISHER charges
RL-112 RECOILLESS RIFLE
M-25 RUMBLER
AT-47 ANTI-TANK EMPLACEMENT
The EXO-51 LUMBERER's main gun
The M5-32 HAV's main gun
The TD-110 BASTION's main gun
The VINDICATOR DIVE BOMB Mk3, AIRSTRIKE, MISSILE BARRAGE, THUNDERER BARRAGE and SHREDDER MISSILE STRIKE will also destroy objectives reliably. Note that ILLUMINATE BEACONS require you to punch through the shield before using these weapons.

SMOKE devices can give relief from enemy weapons fire. They also slow CYBER HOUNDS however they are no defence against other hostiles with melee weapons.

By far the most used STRATAGEM is RESUPPLY. This will drop two ammunition containers in a HELLPOD. Upgrading it to Mk3 drops the ACTIVATION TIME time to 5 seconds, reducing the time that you are sitting around waiting for a patrol to find you. Ammunition containers will generally resupply half your weapon's total magazines, but they will always completely refill a SUPPLY PACK dropped with a RL-112 OR MLS-4X.
The REP-80 is a wondeful tool that will heal HELLDIVERS and repair VEHICLES. The upgraded version has the MULTI-TARGET ability, allowing you to keep multiple teammates alive under heavy fire.

The AD-289 ANGEL and AD-334 GUARD DOG are useful drones that can take some battlefield duties off your hands. Don't rely on them to work just as well as a fellow HELLDIVER though... and that's saying a lot.
The RESUPPLY PACK is a highly useful piece of kit. It stores 2 ammunition containers by default, allowing you to act as a mobile ammunition resupply point. However it will simultaneously regain charges AND refill your personal ammuniton when you pick up an ammunition container, doubling the amount of ammo you normally get. Never feel guilty about taking all the ammunition containers ever again!

The A/AC-6 TESLA TOWER does not discriminate between hostiles and HELLDIVERS. However, it foes not attack OBJECTIVES, making it perfect for guarding static points in BUG-controlled territory.
The HUMBLEBEE UAV DRONE should always be the first to be upgraded. Doing so allows you to discover HIDDEN OBJECTIVES and RESERACH SAMPLES, making missions easier and accelerating the rate at which you accrue RESEARCH POINTS.

Pay attention to the qualities and descriptions of OFFENSIVE STRATAGEMS and consider what perks will be most useful to use with them. EXPLOSIVE does not mean ANTI-TANK.
The PRECISION CALL-IN perk reduces the ACTIVIATION TIME by a flat 1 second, to a minimum of 0.1 seconds. Thus it is useless for the STRAFING RUN, CLOSE AIR SUPPORT and to an extent the HEAVY STRAFING RUN, STATIC FIELD CONDUCTORS and VINDICATOR DIVE BOMB STRATAGEMS.

The SHREDDER MISSILE STRIKE takes exactly 3 seconds to detonate after the ACTIVATION TIME ends, exactly the same amount of time it takes to REINFORCE. As long as a REINFORCE beacon is active, the mission will not fail.

So, that's the great wisdom. Hopefully it proves useful and I have not wasted my time teaching a room full of doomed cannon-fodder.

If you have an amendment to this speech, please contact your nearest HELLDIVER INSTRUCTOR BOT and fill out the MTL-A1 ALT/ADDN form. If you suffer serious bodily injury or dath from following the lessons in this military lecture you are entitled to lodge a formal complaint with your MILITARY PERSONELL WELLBEING REPRESENATIVE.