I`ll say understand the Major Scale first, I mean... really understand that scale.
Its step pattern, type of intervals and how you alter them, making chords based on that scale, what intervals you change in order to get a minor scale, etc.
You have come to rigth place, this site is filled with information, and people who can answer your questions.
In the mean-time, I`ll link you to a thread, we had a while ago.
http://www.guitartricks.com/forum/showthread.php?t=16015