I have a few simple things that I do, firstly whenever I decide I want to buy something I always wait a period of time after that initial decision, let's say 2 weeks, if after 2 weeks I still want it then I ask myself why I really need it and if it will improve my life, if the answer is yes then I'll buy it.
What if its a life changing decision and you need to decide as soon as posible or othet people might get that chance to grab it on your hands. But still that style might get work well.