I like p3 more vs 1 life classes like hero/bh/ARC/mando cause you only gotta land 2-3 shots to kill them (well sometimes more, depends on how much headshot). However against a soldier you need to land 2 shots most of the time to kill them, which sucks. So against soldiers I prefer using e-11.
I like p3 more when my opponents have bad movement. I mean that it's easy to land shots on them. It's hard to explain but like when you are against a p3 user, you can often tell when and where he's gonna shoot, so you can avoid those shots with correct movement. In fact you can do this against every weapon, but it's most effective vs p3 because it's slower fire rate and high damage. (Dodging is just as important as aiming. You could often debate whether a shot missed or was it dodged in this game.)
Other general advice. (I'll be using DOTF examples) -Always stick to your team, if they're timewasting at gen, then you should rather join them than to just die alone and spec their time waste.
-Always check your back, jedi/sith always try to attack from behind. (and often jedi/sith players like to call gunners cowards lol) Doing 360 jumps is a practical way for doing this.
-Check the corners and the walls above you, jedi/sith like to go for ambushes. Be a paranoid if you want to be safe from glowstickers.
-Use teamoverlay. It can tell you a lot. Example, you're an imp at main, and you see your teammate died at t-junc, then you know you're about to get flanked. This is just a simple example, but teamoverlay's information can be used for much more, like for throwing well-timed nades, avoiding unnecessary rage !p from a low hp teammate.
-Know your enemies and know your teammates and their habbits. Example, try to avoid fighting in front of a trigger happy teammate with sloppy aim, they will TK you. If the enemy team has such a player, then try to take advantage of him and get some jedi/sith TKed. Don't be near that guy who keeps throwing obvious TDs at jedi. Be wary of that mando who kept suicide rocketing at the round start for 5 rounds etc.. Prevention is the best way to keep your health as they say.
-If you often find yourself dead too soon, then the best thing is to start doing nothing, just taunt spam at your spawn for a short time or something. It's usually the most dangerous in the 1st minute of the round because of the TDs, rockets, nades and random rushers.
I wouldn't put that much importance on aiming anyway, because in some situations you just need high awareness and optimal decisions to kill even the best players in this game with minimal effort. Also because of the slow bullets that players can dodge.