I go in with a limit. Say like $30. Pick out stuff I really really like and/or know 100% that I'm going to use it. Sometimes I'll go in with a mission: "I'm just going to get fabrics for this quilt and maybe something I like if I can spare it". I figure out the total cost before going to get my fabric cut. If I go over budget I put some things back, fabrics I don't like as much as the others.