I may add some quick pointers but this will not be a full guide at least not right now.

First section map is fairly easy for the most part in terms of combat encounters with the exception of some swarm situations were it may be wise to run through the tide than sticking around to fight.
Drones are sometimes easier to combat while in reverse to keep some distance, as they usually just run right for you for the up close kill shots.
Learning to pilot these subs can be tricky however I have gotten the hang of it using my Xbox One controller and running in Simulator mode. Experiment a lot when fighting to get the hang of things.

This area is not entirely more difficult but can be in sections. Look out for the giant tin can (Naglfar) floating about as it is armed to the teeth. Sometimes you can use this to your advantage if you get too many enemies on your six just glance near the massive ship and let it thin the herd, also be aware there are some cluster drones in this area that can take you with a vengeance. Try Keeping your distance like described in first section. Scuttled subs give very little for salvage but the wrecks on the ground give almost double the value of stuff here. Scavenge as much as you can it piles up quickly.

You can trade up all your collected charts in Spirios for a nice wad of currency, I would recommend using that to upgrade your home base to max for some very useful crew upgrades and specials.

Also dont forget to hit those maze tunnels on this map once you score level 3 sub. Some really nice goodies to be found with some effort.

Thanks to another gamer, DarthSasquatch who took the extra time to make a very nice guide to the maze you can see for yourself if you want extra navigational help here. https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1086827062

Note- Naglfar has many docking locations on its top side with some loot should you manage to take away its bite. Nothing special however just some stuff you dont see very often and ammo.

Arrrr me maity you have become a salty dog fer sure to make it this far.

This area is fairly barren and full of baddys in all shapes and forms. Expect to see a lot of grouped drones here. The deeper you go the more numbers the drones will come in.
The smell things are like a trail to lead you places important. At the Crevasse Edge you will find weapons that are key in taking enemies down. Also you will want as many air tanks and scrap as you can carry because there is little of that in this dark place. If you happen to have lots of currency than you can buy scrap in the encampments.
Be aware that many drones taken down will not provide air like the other maps. The glow pyramids provide a lot of scrap so be sure not to overlook the anchor places to score that loot as well.

One last bit of warning to the deep explorers some sections of this map will act like a trap and have no loot to be found in the deepest parts of the outer depths.