Good Book covers don't necessarily require strong drawing skills:
Bold & legible titles and authors names are key factors!
Thumb-nailing your project is always
the first and most important step!
Next, if appropriate color studies are a good way to help to set the overall tone.
Make sure you plan plenty of space in your design for the Title and Author's name as these are the most important aspects of the book cover!
Watch this excellent video by cover designer Chip Kidd:
Lolita book cover contest and links: http://invertedblog.blogspot.com/2011/06/evolution-of-illustrator.html