The number one problem facing most people who try to represent themselves, also known as appearing pro se or pro per, is that they don't understand the concepts behind what they are doing.
Note I didn't say they don't know the law,because the law changes on a regular basis, I said they don't understand the concepts.
Law school really teaches people concepts more than anything else. The common saying is that law school teaches you 1) hot to take the bar exam and 2) how to think like a lawyer.
The ability to "think like a lawyer" cannot be overemphasized and is not only important, but also a skill that lawyers often lose.
The most dangerous lawyer in court (to the other side) is not the one who knows the most law. There are lawyer out there who can quote cases, cite statutes, and carry on conversations and write articles on legal topics that are impressive. These same lawyer are quite often absolutely useless in the courtroom because they know what a court ruled but don't understand why it ruled that way, so they can't quickly apply the law from one case to the facts in another.
In our Guerrilla Guides to the Law, discussed here, we emphasize this point.
When you are faced with case law or a ruling from your court, sit back and try to figure out what is the main reason behind what the court ruled. Don't get caught up in all the legal terminology, just remember that, overall, the law wants to be fair and so why was this decision fair under these facts? And, how does it change under your facts? If it was a ruling from your court, why was it decided that way? Did you not point out something important or, more often, did you focus on something you thought was important but the judge and often the other side, thought was unimportant?
If you are looking at a statute, ask yourself why the legislature enacted it? What purpose was behind it?
Once you understand why, you are miles ahead of your opponent.