While deciding the best products to promote, you may need to do a research on the best products for your next campaign. I found some people learn related to reverse engineering by reading a course of Barry Canvas. By knowing related to this knowledge you can cut your research time.
Some others are using facebook search and finding a groups or facebook pages that owning an e-commerce or an online shop website. Nowadays you can take a look of their campaigns (paid) by visiting their page and following on their Page Ads section. You can take a look of the current advertising campaign that runned by internet marketer and then you can also take a look on the products link that provided on their advertising sales copy.
You can take a look also on the marketplace. What products are booming todays or what products will be coming to trends within the days or this week. This can be done by using your analycal thingking or you can also take a look on some tools that can give you analytics on various marketplace for both local and international marketplace like amazon etc.
Whatever methode you choose, I will suggest you take a look at the course who will teach you related to reverse engineering in internet marketing on this era.