The rules of field ships in Eve.
Rule #1: Fit a ship according to its bonuses. In general, not fitting according to bonuses will pretty much make you near to useless (there are exceptions, but not many). You will actually be a detriment to your fleet because the FC will likely expect a certain class of fitting and you not following it may lead him to put you in situations you are ill-equiped to handle.
Rule #2: T2 guns before T2 ships. A T1 hull with T2 weapons is more effective than a T2 hull with T1 weapons.
Rule #3: Bring what is needed to a fleet, not what you want. Being successful in Eve is all about how well you cooperate with others. This is contingent on how good you can fly the ship of course, but don’t bring a Drake to a HAC fleet or a Sniper Fleet. If the FC needs an inty, and you are available, bring the inty. If the FC needs more snipers, and you can fly them.. then you bring them. In the end, your choice will help improve the chances of the entire fleet.