I have worked with many graphic designers, most are average and some even great designers (better than I) and with all of them I had to give them pointers on how to fix the up their banner. It’s not rocket science (but it is a science) and quite simple once you understand the goal of the banner.
The goal – get a simple message across quickly, effectively, and emotionally. These are the principle of a great banner design and like all principles, once you understand it then you can break some of the rules
Principle of a great banner design
Big Attention Grabbing, Can’t Ignore Headline – make the headline
One Attention Grabbing, Can’t Ignore Image
High contrast colour scheme
Call to Action
The visual hierarchy (what order people look at) should be: