First bit of advice are the dreaded titles.

1) Do not forget to capitalize correctly.

Bad example: the girl and the cat
Bad example: The Girl And The Cat
Bad example: the Girl and the Cat
Good example: The Girl and the Cat

2) Do think long and hard about the name.
DO NOT just come up with a half assed name like,
The Host Club and the American
The Basketball Lover with the Basketball Team
The Manager with the Volleyball Cuties
Yes. AND?!?

3) Do not use a screen shot as a cover, it makes it less appealing.

What would you got too?

This?

Or this?

3) Make sure to put the title and author on the picture like this

And add the fandom it's in to gain attention.

Well that's all on titles and covers...

I think...