The best method is
1.Scan other stores of dropshippers.
2.Collect Some Items That Sold More Than 3 Times In Month
3.Extract the best niches get some ideas
4.Check Competition In eBay
5.Find other similar items in Aliexpress,Banggood and other websites.
3 parameters important points
- Check How Much Competitors
- Items That Sold More Than 3 In Month
- You Can Sell In Profitable Price Relative To Other Sellers