Do this for each of your keywords and look at the results. If all of your top keywords have a Monthly Search Volume of 5,000 – 10,000, you’ve definitely got a potentially profitable niche. If you’re too much over that up into the high hundreds of thousands of Monthly Searches, you might want to get more specific with your niche rather than competing with much larger, established websites on more popular subjects.
The one constant with trends is they do not last. They are always based on a new technique or technology and follow an interest cycle. Since human beings by their nature move on to something different, new and perceived as better (and usually ACTUALLY better), if you are attached to any one trend, you are doomed if you don’t adjust and keep up with the times.
Selling private ads can come in the form of banners, buttons, or links. You can even make money writing sponsored posts where you write about or give a review of an advertiser’s product or service. Another option is to write an underwritten post or series, which is where you can write about any topic, but the advertiser pays for a “Brought to you by” mention in the content.