In software engineering, an anti-pattern (or antipattern) is a pattern that may be commonly used but is ineffective and/or counterproductive in practice. – Wikipedia
If you go to that Wikipedia article, I discovered that you'll also find a very good list of common anti-patterns. I really recommend that you go read them. Familiarize yourself with them. I've seen several of them in projects I have been on, and I have most definitely fallen for several of them myself as well.
Knowing about anti-patterns will most likely make you a better software developer and if you're a software developer, I sure hope you wish to become better at it! I guess some people might not want to get better, but I sure do. And if you feel the same, go now and read that list 🙂