do it the other way around: start with a blank screen and start adding the controls from your crowded screen, thinking for every one of them if you really need it and throwing it away if not. this process also makes sure you are exhaustive, you consider each element and don't forget weird controlls in weird places (of course, the ideal would be to start from a blank screen and a vision of what the user needs to see and do - but lacking such a vision a "cluttered mess" --> filtering --> "blank sheet UI" process helps a lot)

EDIT: + do it the pen(cil) and paper way, and implement a mockup UI only after, it really clears your mind from the "this should be here because that event expects..." crap you end up thinking about when the interface is implemented the "lipstick on a pig" way - for web, think tangled mess of HTML & Javascript DOM manipulation + unimaginable PHP horrors on the server site