First of all, product need to meet two criteria:
Product need to solve real problem
People do not have seen this product in store like amazon, walmart, etc because if they have seen the product in store. They will purchase from their.
Now we need to look at Facebook/Instagram ads which are heavily promoted because this means that product is making them lot of profit.
Manually finding the products can take time. We have got websites that make this process very easy.
They actually provide you the Facebook ads that are running, dropshipping website and also data on how much it is selling.
These websites are paid but worth it.
From here, things get simple. Find the winning product from the above criteria, build the dropshipping store on Shopify and run Facebook ads to the store.