Placements are the first thing to look at. 1. Your ad is likely to be showing up on mobile, and many apps are designed to make people click on ads by accident. 2. There is a ton of click fraud on display, so you should never optimize for clicks. I found that Smart Display optimizing towards conversions works well. If you do not have a solid conversion setup or conversion history, make 3 pages per session or 60 seconds per visit your conversions and optimize to that.