Destroyer Droids are notorious for being able to tank damage and kill you with only a few shots.
They are equipped with rechargeable shields and dual blasters. Grenades just bounce off their shields.

So, how does one stop a Droideka? Well, the easiest way is to shoot it with a tank, but some maps don't have vehicles. Switch to the regular Trooper class, and when a Droideka rolls up and deploys, crouch, find some cover, and continuously pour blaster fire into the shield until it goes down. Don't worry about reloading, most ai stop shooting you the moment you reload.
Now that the shield i down, you can focus upon the droid itself. It should be easy to kill, only a couple of shots and *poof* no more Destroyer Droid. They have a hard time turning to face you, so if you don't have cover, you can just run around behind it and shoot it.

Wristrockets on a Super Battle Droid (SBD) are known for their ability to kill a player in a single shot.
They also cause damage by being near them as they shoot on by.

The only way to counter them is to crouch and roll out of the way. The SBD takes a second to switch back to regular blaster fire, so use that to your advantage in order to destroy it.

Get The Hell Out Of The Way And Grab A Tank Of Your Own!