First of all I make sure if I really need it, not just to buy it and never use it. Then if I want it for example, suppose i want to buy a mobile , I check for the specification that I am searching for and to be from a reliable brand .
after I check the specification and decide what exactly I want I check for prices in more than one place so that I will not be cheated. When I find the best price and best place to buy, then I buy.