Believe it's not easy as it looks. It took me months, but as to your question. I just use adwords keyword research tool or another one on the internet. Then build out my campaigns. Sometimes you'll have to rebuild them out 3-5 times before you get it if not more (way more). There ain't much I can tell you out of all honesty accept for test and test. You just have to make good sense of the market you in because every one is different. There is still ones I struggle with today that I know are profitable.