Hey guys this is SpiderWoman- . The best types of covers are the ones that are eye popping and really grab your attention. One of the ways to make a cover stand out is what I refer to as a color pop.
Example

What I did is very simple and you can do on most photo editing apps (I used photoshop mix) I put on a black and white filter and then erased around the hair. Other examples are

It's best to do with bright colors. You can do this with other filters as well its a simple and easy way to make your photos POP.

Yours truly,
LeagueofGraphics