I was lurking around the Kindle Authors forum on Amazon, and I came across a posting by an author who didn't understand intellectual property rights. She had found out too late (after she'd published) that she was using material she thought was fair use and public domain, and she was now open to possible lawsuits. She was scrambling to fix the problem.
If you design your own cover (or if you use your friend or cousin) be SURE you understand the ins and outs of copyright law. Free clip art (such as those that come with Microsoft or Adobe products) is often restricted to non-commercial use only. Sometimes the licensing is not clear on the package.
You can't just go grab anything from Google Images (most of those images are under copyright). Even if you use Wikimedia Commons - or other free use sites - many of those images have restrictions on their use. In some cases, the copyright holder may only want credit. In others they may restrict to non-commercial use. Others want to be contacted before permission is given. Read the fine print. If you don't understand it, move along, or contact the artist.
And whatever you do, don't use song lyrics in your work. "Fair use" with songs and poems is VERY restrictive, and the music industry is very strict on enforcement. Paraphrase. Describe. Don't quote. (I'm told that you can use up to seven words, but I am not a lawyer, so I cannot give this advice as fact.)
The advantage of traditional publishing is that you have professionals who won't make such mistakes themselves, and they may help you catch any stupid mistakes you make, from a legal standpoint. When you self-publish, you are on your own, and you need to pay attention to those factors.