Now I find that I buy things from pure necessity. So I've learnt to be patient, try living without something for a while (e.g. I think I need new jumpers, but first I deal with just wearing the warm clothes that I have for a few weeks) then if I find that through necessity I absolutely can't live without something (all my jumpers are in the wash/aren't warm enough) then I buy it. I don't enter any shop without a purpose!