I see alot of questions floating around, mastering is a tricky subject. Theres no right or wrong, just personal experience.
Heres some reading material, the most recommended to my knowledge.
The secrets of the mastering engineer by Bob Katz. Small download definetly worth the download. Make sure you share it with others as well.
ftp://205.250.213.144:58/secrets.rar
this site is also very useful to me, if you post with a question there youll some some class act replies
http://www.serious-sounds.net/index.php
enjoy