Are you using CC? Unless you're running Guardian/Shadow/Vanguard/NotASmuggler or the Empire equivalents, your group should have at least one method of keeping an enemy out of a fight for a minute at a time.
Commandos can Concussive Round anything.
Sages can Force Lift anything.
Sentinels can Disable Droids.
Smugglers can Slice Droids.
Scoundrels can Tranquilize non-Droids.
a common thing i see is that people ruin the cc. several times i've cc'd something (Assassin mind trap) and the group clearly sees me do it but still aoe and attack everything. especially the tank. decides he's wonder tank and pulls just because. we don't wipe but sometimes people make it harder than it really is.
just do like somebody above said: tank the strongest thing(s) and let dps handle the others.