Shield bash is an interesting ability that was created to help keep players from getting cornered by big monsters.

The shield bash animation shows you raise your shield and then boost forward a short distance, anything in your path will take a small amount of damage, get pushed away (except for naturally immobile enemies) and will be stunned (a few monsters are immune to stun).

Not do:

This shield bash shows you raise the shield but in reality you can still take damage. Hazards include: dashing into attacking enemies, bullets, rockets, exploding blocks, status and spike traps, shankles, and wisps.

The Shield bash also pushes enemies so if you aren't in danger try not to use it too often, your teammates rely on the predictability of certain monsters and bouncing them around can mess them up.

Shield bash is capable of doing damage but don't rely on it to help you too much.

The stun status slows down enemies and their attacks but it does not slow down projectiles, so don't be surprised if a rocket puppy fires off a full speed shot while stunned.

To do:

If you get cornered or surrounded then a shield bash can save you hp, you may take a hit while escaping but it is far better than being stuck in a sea of enemies.

Keep the Dash ability ready in case your shield bash turns out to be a bad move, that way you can hop out of danger.

Wait till your enemies aren't in an attack animation to shield bash them (this can keep you from losing hp).

Shield bash takes up %50 of your shield, if you shield can't take a hit with that much health then you need to be really selective about when you use it.

Shield bash can only be used when your shield is at %100, try to anticipate when you are going to get trapped and if you can't see a way out prepare to shield bash before the monsters wear your shield down (because once it takes a hit you can't shield bash till it is back to %100)