For those who like concrete details and instructions, you are in luck there are rules I like to follow. For those who don't, you are also in luck, because as you already know, rules are meant to be broken from time to time.
Ok, lets get to it! One design rule I always follow is to make my photos pop by either matting, outlining, or highlighting the edges of the photo or LO. Regardless of project type, whether digi, physical, or somewhere in between, I would follow this rule of thumb. After all, it is the person I am memorializing that I want to shine in my LO, not the kits. Here are some examples: