So I am diving into affiliate marketing and this is how I start; I chose my niche as weight loss, good for starting, many products - I will buy a domain, probably .info (cheap) - Find some keywords, (aiming long tail) and write (pay for) articles about those keywords - Submit articles to the article directories with a link to my domain - Publish new posts on the domain with links to the products - Do this every week with a new domain ( invest what you earn for a while ) Correct me if I am doing anything wrong.
Unless you plan advertising your site, I don't think weight loss would be a niche that is "good for starting", as you say; there is a ton of competition, so you'll get very little search engine traffic.
I can't find one for you, but I suggest using the google keyword finder (I can't post links yet) to find a niche that doesn't have too much competition, but has at least 5,000 global searches per month.