First of all, a video on using YouTube.

Then a video on checking out you niche in Google. Notice if there are many affiliate programs in the organic results on the left. Look at the Adwords (top & right) to see who is advertising, and how many of them are affiliates.

Note down the affiliate programs you’ve discovered for you niche market

Then check out your niche market on Google Trends . Note the volume of traffic, and whether its seasonal