Mixing tracks for an album is no small task, but make sure you’ve done your homework before getting started. Keep the big-picture of the album in mind by listening to every track all the way through. Decide if the so-so tracks need to be cut, or maybe just re-recorded. By starting with a good set of tracks, you’re setting yourself up for a successful mixing session.
You can read more mixing tips here: http://therecordingrevolution.com/2013/01/04/3-things-i-do-before-every-mix/