I use the "treasure hunt" method. I think about something I don't have much of and look for that. One time it was bright yellow and orange fabrics to make fish for my bathroom. Another time it was bright aqua for a baby quilt. This way I buy only things that I have a purpose for and don't end up with a lot of misfits, compulsive purchases and empty checkbook or full charge card.
Every so often I might give in if it's something I haven't seen before or can think of a project for it, but not very often.