Masterings a really touchy thing unless you gota rediculosly good setup and years of experience. I managed to **** up a few mixes by not knowing what i was doing. But having said that, you should try using izatope`s "Ozone" mastering plug-in. If you use it right it can make a really big difference. One thing i always do now is pick a track that is similar and very well produced and constantly compare my track to that as i master. That way you can judge how much exitation or widening is needed and not go over the top, which is always the problem. Hope this helps.