If you have ever work with fb you know classic rules of making good ad picture.
1) Your banner must comply with the facebook rules which are depends on ad format.
There is only 1 rule which applies to all ad formats: 20% text - you know about tool for checking it.
But I want to give you an advise how to set up the text and image.
When compiling an advertisement, it is necessary to take into account the spatial positioning of images and text. These elements must coincide with the anatomical features of your visual pathway.
The object arising in the left field of view is initially projected and processed by the right brain (arts), and the object arising in the right field of view is projected and processed in the left brain (logic).
So, thats why you should to set text on the right and image on the left.
Thanks for reading my post. May your profit be always high :)