Are you dying?
Are you dodging AOEs?
Are you getting hit by stupid shit you should of easily avoided?
Have you read up on the respective "official" threads of the DPS job you're using and can press a rotation?
Can you still perform said rotation whilst dodging AOEs and performing mechanics without failure?
Are you parsing, on a dummy, around the average DPS of said job under certain iLvls?

If you check yes to all of above, you're doing better than 70% of players already and I'd say your performance is good enough.