choose and target a specific keyword(atleast 2 words long), use any keyword suggestin tool ("adwords keyword tool" is free,market samurai is paid but recommended) , and check how many searches are made for that keyword, choose a keyword with less than 20k monthly global searches, they are easier to rank.
than make a website about that.
possible top paying niches- health (asthma, cancer etc), insurance (auto insurance in your state/city, health insurance), Reviews (product reviews like mobile phones,bikes,file hosting,software,antiviruses etc) and there are many more niches.
wordpress or blogspot recommended.
You must work for 2-3 months to get in top 10 results n google search, depending on the competition.