One of my favorite topics to write about is weight loss. Although it is difficult to find key words which work well in such a cluttered niche there are always a few gems hanging around for the diligent researchers. The phrases "How to make the XX diet work" or "Why am I failing on the XX diet" are good starting places to search on google.
Folow these easy steps:
Pick a phrase
Google it exactly with quotes
Tweek the phrase
Google without quotes
Write an article about the site with the title being your google phrase
Include hoplink at the end of the article
That's how easy it is. You could write probably 2-3 different diet articles every day on a different one and you'd still have something to write about after a month. So dive into those dieting websites and find a niche for yourself!