Environmental awareness. Do a head count of enemy players, if you're heavily outnumbering the other team, head over to the other node. If someone's solo guarding, try keeping an eye on his/her healthbar (you can focus target), or if you see your teammates running around like crazy around a node on your map that usually means they may need backup as well. In fact, most of the time you don't even need someone to call incoming to know where you need to be.
If you DPS with a tank class, use your taunts anyway, it helps a lot.
Don't chase a solo kill if it hurts the objective.
If you notice your healer is in trouble, help him out.
When someone's capping a node, don't "help" him cap; instead cc incomings.
Don't break cc when someone's capping.
If possible, don't los your healer.
Don't leave a healer behind to guard a node.
During huttball, make sure you're not standing in a position which allows the enemy to leap to you and score. Keep your ramps clean and hold mid.
Don't try to 1 vs entire team. Especially during Ancient Hypergate, don't pointlessly feed the other team kills.
Don't mindlessly DPS; keep an eye out on the node.
Well, I guess all this doesn't make you great, it's just common sense really