I onced talked to someone who said that they were making big bank with adwords. I asked them how and they told me the same thing that I have read everywhere else. Do keyword research and test campaigns.
Testing is where the problem comes in. There is an old saying "It takes money to make money". I can't speak for anyone else, but I have lost lots of money by testing campaigns and don't have anymore to give to adwords.
I even read where one may have to invest $1000 in testing ads on adwords before finding a winning combination. Since losing money and reading this information, I decided that I don't have $1000 to test adwords ads campaigns. I nodded my head and walked away from adwords.