Maximize the amount of time you're dealing damage, minimize the amount of time you're taking damage.

What this means: shoot people in the back and in the flank. When they start looking your way, back around a corner or behind a pillar to break line of sight. If you have a teammate fighting that opponent, rush back in to shoot them in the back/sides even more right as they start looking at your teammate again. Be swift so that your teammate doesn't take too much damage or die. Use the LG/rocket launcher for this unless you're too far away to do so. Just make sure not to hit your teammate since that will throw your teammate's aim off and make it easier for your opponent to hit him. Done perfectly, neither you nor your teammate should have taken very much damage at all.

If the enemy is alone, after you run away, rush to a different entrance as quickly as possible (use sideways rocket jumps for maximum speed. If you don't know how to perform sideways rocket jums, check out this video by Rocket Jump Ninja) and shoot them in the back/sides again. The best gun for harassing enemies like this is, surprise surprise, the railgun. And it is no coincidence that the best CA players (like k1llsen, v1um and silencep) have amazing railgun aim. It's quite simply the best weapon in CA, though you still need to be equally good with the other two to win, since most of the fighting, especially at the start of the round, is done in close quarters.

If lots of enemies are still alive it's usually a better idea to find another enemy instead of going for the flank, because the other enemies aren't at that moment trying to kill you specifically and - this is the important part - they might be busy trying to kill one of your teammates. You want to be shooting the enemies fighting your teammates as much as possible. The reasons for this are many, so watch the indicators on your HUD that show where your teammates are (you do have them on, right?) and keep your ears sharp for sounds of fighting, and abuse sideways rocket jumps to move quickly. Do not use vertical rocket jumps; vertical rocket jumps are slow, make you fly high up in the air, and you're just begging to be LG lifted or railed by multiple enemies at once while doing them.

NEVER pick a fight against multiple opponents. If you end up in a fight with multiple opponents shooting at you, the first thing you need to do break line of sight. Do this as fast as humanly possible while avoiding walking into their rockets (assuming they're not all using LG, which they might be). If possible, try to keep one enemy between you and the other enemies so that their shots will hit their teammate instead of you. Don't forget to shoot at them while doing this, of course. Rockets are generally a better choice than LG here, even if they're not really close to you, since rocket bounce will throw their aim off and splash might damage multiple opponents. If rockets are hard to hit in that situation, use LG. If their numbers are really great then you can also use plasma.

If you have a good team that gathers at the start you want to make sure every opponent present at the gathering point with you is in check. What this means in simple terms is that none of your enemies should have nobody shooting at them when the countdown hits 0. ESPECIALLY not their MVP. In fact, if their MVP is significantly better than the rest of your enemies you want to be less strict about checking and try to focus fire the guy to death instead (i.e. have more than one person shooting at that specific guy). While this is happening the "running away" part of the first paragraph does not apply until your health gets too low (around 100-ish) and you know for sure that your opponent has more health than you. If your opponent has less health, don't run, just kill him even if you end up with only 1 health left, unless the opponent is significantly worse than you and you just got hit by unlucky rockets or something. In that case your HP is more valuable than his life and you should run and start railing. Remember to be quick; the slower you are the more damage your teammates will take. The round can depend on single seconds.

If you're fighting the MVP and are not yourself more skilled than their MVP then you don't run away at all. You deal as much damage to the MVP as possible until you die, all to maximize the chances of your teammates successfully killing him later.

The reason you need every opponent to be in check is that an unchecked opponent is free to shoot your team in the sides or back, when you or your teammates are not focused on him and not dodging his shots. And he's free to do this while having no need to dodge himself. Not having to dodge means he's free to focus entirely on aim, and that means he can easily do the damage of 2 or even 3 players all by himself. Your team will melt.

There is an important exception to this checking rule, and that is if your team is on one side of the gathering spot and the enemy team is on the other side. In this situation you and your mates will have no enemies behind you/at your flank, and are thus able to dodge them just fine. In this case the best strategy is for all 4 teammates to focus fire one enemy at a time. Optimally you should focus the enemies down in order of skill, highest to lowest, but more realistically it will be from closest to furthest.

Once the gathering spot has been taken it's time to go on the hunt. Having taken the gathering spot means you have map control. Map control in Clan Arena is about having freedom of movement. In essence, you're free to move around most of the best spots on the map as quickly as you feel like without having to worry too much about getting hit by railgun shots or spam. Use this advantage, but make sure you don't stupidly rush into a group of enemies and get ganked.

Staying at the gathering spot after you've already taken it generally opens you up to enemy spam and rails. However, if you're playing on a regular CA map but are not playing the standard 4v4, but instead 5v5 or even bigger teams you might not have a choice, since at such large teamsizes any and all entrances to the gathering spot can be covered by grenade and rocket spam (this is why high-level CA is played at 4v4 or smaller rather than 5v5+). At big teamsizes (6v6-8v8) you want to take both the main gathering spot and one of the secondary "camper" spots, since if everyone tries to take the gathering spot they will be swimming in grenades. Spam is murder to crowds, so spread out a bit (just don't be alone. You still want the numbers advantage). Also, if you manage to find a decent railgun spot when the teams are large like that (I'm assuming your railgun accuracy is good here) you can expect your points to skyrocket to 120+.

If your team gets pushed off the gathering spot, or your team has one too many lone wolves you want to spam/rail the enemy as much as you can if they're camping the gathering point. If they're on the hunt you want to use divide and conquer tactics if at all possible. People often have trouble sticking in groups while hunting, since they don't pay enough attention to the sounds in their headphones. Try to catch them with the LG while they're jumping off platforms, rocket them while they're coming around corners, find flanking positions to take sneaky railgun shots, and always, always refer back to the first paragraph: Don't take too much damage, and don't let your teammates take too much damage.

This simplifies to: shoot the enemies shooting your teammates.

And remember, your performance in Clan Arena, just like in FFA, is highly related to how good your aim is. If you're missing your shots, you're not dealing damage. If you're not dealing damage, you're not being useful and your teammates are forced to pick up your slack. And remember the thumb rule for weapon switching: close range-rocket, mid range-LG, long range-rail (finishing a low health opponent-shotgun/HMG/MG).