before starting a blog for adsense, how do i choose a the best keyword? I even cant decide which product or service to write about. I mean how do i choose the keyword for which advertisers are paying google.
You have to decide about one keyword then use the google keyword tool and try to estimate the monthly traffic for it. Now use the keyword tool for the average ppc and if you can make serious money. Go to google and check the top 10 results with the yahoo site exolorer about there backlinks they shouldnt have more than 200 backlinks. Now you have your keyword - build a nice looking website with at least 400 words of content and get every week 20-30 backlinks for it and own the rankings
According to your condition(how many ours you can work on your website, do you have any related free blog running, you're are specialize in what, etc.), then with the help of those keyword search tool, find a suitable keyword.