Collage can be easy for Everyone!
I think of a collage like an Ice Cream Sundae
The Background (Ice Cream) is about two thirds of the collage, it is light, has low contrast and doesn't have many different colors.
The Focal Point (Topping) is Large and easy to see.
The Details (Sprinkles, Nuts, Whipped Cream, Cherry) and sprinkled lightly to create interest.