Ecommerce Product Niche Research Help

Hey guys I've been a long time lurker here and finally decided to reach out to the community for some help. So i've started to get into ecommerce and i'm at the product research phase. I've been using the ecommercefuel ebook as a guide. He's basically saying you look for long tail keywords in the 3,000 - 5,000 range. I'm looking for something to compare his methods to. Does any one have any recommendations or advice?

Thanks!

I will follow