Depends what type of quilting you like to do. If you do scrap quilts or applique or smaller projects like table runners, you may just need smaller pieces like fat quarters or half yards. If you are making bed sized quilts and want a piece for the border, 3 yards is a good number. If you find a piece you would like to use for a backing, it can take 8 - 10 yards for a queen or king.
Not much help, am I????? LOL
I once heard someone use this rule of thumb.... "If you like it buy a yard, if you love it buy 3 yards, and if you can't live without it, buy the whole bolt!!!"