On Facebook everyone want to get attention, therefore your advertisement have to be attractive, interesting and encourage people to take an action.
I found that collage works very well to me. CTR is much higher than simple picture. How do I create collages for my ads?
Usually I use PicMonkey.com, I already wrote about that How to create pictures for ads? As well, here is simple to choose necessary format ant picture size, easy to experiment with picture size and find the best one for your collage.
Facebook ad format is 1200 x 628
As well I like to add some text on ads, which inform customer about the product or engage them. The best way to engage the customer just ask the question.
You should know, that Facebook allows to add not more than 20% of text on the image.
People like to see beautiful things. Because of that, I recommend to show beautiful girls, kids or animals on your ads.
The most important thing, that you have to test, which picture works the best for you.