My two cents:
No more than three colors - Make sure there are no more than three colors on your entire outfit (shoes and belt included!). This is a good general rule to obey.
Belt and shoes must match - Okey, I don't know if this really is that important, but it's the most common advice given in pick-up related material when it comes to dressing.
Use clothes that fit your bodytype - If you're a skinny guy (like me), don't use baggy clothes, and if your fat, don't wear skintight stuff.
Hat - A hat is always a nice thing. I'm not talking a Mystery-sized tophat here, but a nice fedora works both as a peacock and a nice accessory.
Necklace, rings etc - Make sure it's somewhat original, not run-of-the-mill stuff. Things from streetvendors are preferable to anything bought in a jewelry stuff (Just make sure they don't LOOK cheap!).
The shirt and tie - This is always a killer combo, as very few guys use it when they're out clubbing (makes them feel "overdressed" I guess). Make sure your tieknot is loose and that the first buttons in your shirt is open (to show off your awesome necklace
)Colors - Don't be afraid to add colors to your outfit. A yellow shirt is preferable to a black one. Just don't go overboard.
CLEAN shoes - Shoes are one of the things chicks notice and we guys couldn't give a rats ass about. Make sure they're a) clean and b) matches the rest of your outfit.
One of the side-effects of gaming is that guys turn into chicks when it comes to getting ready for a night out. Before I would spend like 10 minutes getting ready, now I spend two hours just debating which shirt I should wear!
FEDSTER! No shit, plus now I'm spending time using cover-up makeup to remove those last minute zits that the facewash didn't get. Not to mention calling your friends saying, "Should I wear the xxx shirt or the xxx shirt?" 