My main approach is setting a cash budget, and shopping with cash. Leaving credit cards and checkbooks at home. (Just like others have said).
I personally avoid going to quilt stores. I have unsubscribed from quilting store emails/flyers. They are both HUG temptation points for me.
I'm currently participating in the fabric moratorium (on this board). It's been going since November last year, and ends this November. There are a number of options, depending on areas that you want to focus on. It doesn't need to be a "don't buy at all" approach.
My preference is to purchase backing, batting and a small amount of fabric to finish WIPs or other projects purchased but not yet started.
Some have decided that they will spend when really good sales occur. "Really good" is dependent on their own budget.
I'm afraid the only real answer is self constraint. But in that you can express great creativity with the resources you already have.
Good luck.