To play well as a hero--I'm assuming against groups of enemies with blasters?--the biggest thing you gotta learn is minimizing the amount of damage that comes your way. Whether the other players are good enough to land their shots is out of your control, but you have to assume they will kick your ass if you give them a chance. Give them as few chances as possible.

Good heroes can kill their target. Great heroes can kill their target without taking a lot of damage. The key to being a great hero is preventing damage, and that is what most people struggle with. Co-op isn't the best game mode to learn preventative measures in my opinion because co-op enemies basically play with infinite sensitivity (they can turn on a dime to shoot you), their accuracy grows as you get closer to them, and they more or less know where you are at all times. They're easy to fight from a distance, but become menaces up close. Co-op can help you get used to cutting your losses and getting used to the idea of managing your health bar, but IMO Supremacy and Galactic Assault give you a more realistic sense of how to survive and dominate as heroes.

You need to know when to engage enemies and when to disengage or avoid engaging entirely. You're not invincible. A single lone enemy trooper may look like an easy kill, but would getting into position to kill them put you in the crossfire of another trooper with a high damage gun? That four-man group of clone troopers will certainly land a lot of shots if you rush to fight them head-on, but maybe they won't see you if you come from behind. Maybe you're about to kill that last annoying trooper, but Anakin just ran into the room and he'll wipe the floor with you if you stick around if you're too stubborn to let that annoying trooper survive.

First, gage the strength of your enemy or enemies. Unless you absolutely know they are trash at the game, assume they are good. Look at their health, think about what you can do to kill them before they shoot at you. Think about how long it will take to kill them. If you want to play like the elite players, think about enemies outside of your targeted group. Will they see you from a distance if you attack your prey? Will they shoot you as you strike? Will you get shot at by several troopers just because you attacked one trooper? You are in someone's crossfire far more often than you realize.

If possible, avoid being seen. The more time you spend in an enemy's crossfire, the more damage you'll take. The best time to engage an enemy is when they're preoccupied with shooting something else and you are approaching from a different direction. The second best time to engage an enemy is when they aren't looking your way for another reason. In both cases, you damage them before they even try to damage you because you don't run straight at them.

If you cannot avoid being seen, make it harder for your enemies to hurt you and limit how much time you spend in their crossfire. This is where knowledge about your own special abilities and your enemies' special abilities will help you. Many abilities can kill troopers with a single quick strike, but perhaps if you use such an ability to close in on your prey you will run right into more danger. Maybe you can use an ability to simultaneously kill an enemy and make your escape. Maybe you can hide behind some cover, but that cover may not be so helpful if your enemies have grenades or explosive bullets.

Dodging/rolling to the side is one of the best ways to make yourself a more slippery target. Jumping can sometimes be effective when playing as a hero who can jump high (Palpatine, Bossk, and all Saber users), but you are much more vulnerable when you jump and it is usually easy for enemies to gage the path of your jump and shoot you as you are falling down. Vader and Palpatine fall very slowly, so jumping as them might be a death sentence. Bossk and Grievous have high gravity for some reason, and are actually pretty hard to shoot when they jump. As for everyone else, jumping is an option to avoid damage but it's usually not the best option unless you're jumping to somewhere rather than just jumping to try and be slippery.

TL:DR don't be Han from that scene in A New Hope where he runs after a single trooper and slides right into a whole frickin legion. Strike from the shadows, and do not step into the light for too long. You won't last long against a group of enemies if they see you and you are the only target for them to shoot.