Although there are a wide range of products available to help you master your music, the most important tools are your ears! Taking the time to listen to each track both out of context, and in the context of the other material it is to sit with, will enable you to see the 'bigger picture'. It's amazing how many artists don't hear their tracks back to back until the CD is in the shops! One last piece of advice - it's easy to add more compression and EQ later, but it's much more difficult to take it off - when it comes to mastering, subtle changes are usually the wisest.
Thanks for reading, we hope this guide has left you prepared to master your audio!