What I do is to search online hobby shops for kits that I want to build. I then made a list of kits I like. Then watch the online shops, ebay, and local stores for their sales. If a kit goes on sale or is offered at a good price, I buy it. I now have a small stash of about 20 kits to build.
Once you have a stash of kits you can then decide on which kit to build next by what you feel at that momment.