Mistake #1: Not targeting the right audience. The right audience can be the difference between a successful ad and an ad that brings in no results. It is always the overlap of interests that is your optimal target audience. You should narrow down your audience as much as you can until you are at about 500K audience.
Mistake #2: Having really poor product pages. You may have a really great ad but a really poor product page. One thing everybody needs to know is that an ad is not responsible for getting sales. The ad is responsible for getting the customers to the product page and the product page is responsible for getting sales.
Mistake #3: You make changes in the ad campaign way too often. You should try to let the campaign run for a while, only letting it run for a day or two and driving conclusions from that just isn’t right. If you see good results in one day and drastically increase your budget on that campaign you have a high chance of letting Facebook burn through your money with zero results.
Mistake #4: You do not retarget. Retargeting is very powerful, it is always cheaper to target an audience that already knows you. But be sure to retarget your existing audience with a new ad and a special offer