For a prime example of this- check out the stock tanks for African Cichlids and South American Cichlids. Suddenly, fish that are supposed to be super-aggressive look utterly passive when they are kept at such high populations and are unable to establish any sense of territory or pecking orders.
Definitely watch how much you feed, because clown gobies really don't eat much compared to other fish, so take it easy at dinner time. To compensate, be a bit more aggressive with your water changes that you would usually be.
I have seen clown gobies be exceptionally aggressive with one another, particularly in a small tank. However, to cheat this, I had also seen people using their natural behavioral patterns to their advantages. Clown gobies generally perch among large "thickets" and "bushes" of Acropora, in groups of 5 to 15. In tanks with large Acropora colonies, people generally have the best luck with keep clown gobies in larger groups than breeding pairs or solitary individuals. If you do not wish to keep Acropora, you can cheat this with fake corals or, even better, reef rubble with a similar, bush-like structure to Acropora. By offering plenty of perches, it seems to mellow the clown gobies out a little.
G'luck!