Secondly you should keep the design simple. This can sometimes be difficult to achieve but a simple cover is actually very appealing. It convey a message to the potential reader in a very quick and direct way.
Third - You absolutely must show your cover to other people and get their opinion. What looks good to you may look not so good to others. And worse, it may not convey a sense of what the novel is about.
Fourth - Always pay close attention to the publishers guidelines for cover art. Opt for the maximum allowable resolution. This will give you the best looking cover. There is nothing worse than a cover that is slightly blurry or faded.
Finally - If possible you should never approve your novel for printing until you get an actual advanced copy in your hands. You have to get a real book and take a good look at it. What looks fantastic on the computer screen doesn't always look good printed.
Here is the self designed cover for my second novel called Lion's Last Kill
The Design is simple and straight forward. The claw marks make it look like a lion has actually torn the cover. This effect took me a while to a achieve but was well worth the effort. Other than that the cover has a title, authors name and the tagline "An Epic Fantasy Novel" The fact that the cover is very individual is a selling point.