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.
We had similar way of deciding to buy a things. Only that i dont wait for two weeks. It only took me 30 mins or an hour to decide to buy . First , i have to think on how important should i buy a particular stuff. Second, have to identify if it is a need or just want. Lastly, if it is worth it to spend a money for a particular thing and my budget is enough to spend it.