Excerpt from The programmer who programs least, programs best.
So, how can we mitigate this issue? The obvious way is to write less code! Now, I'm not saying that you should be lazy and start programming less, I am saying that every time you add code to your application you should do so consciously. While you are adding code you should be conscious of whether you are repeating functionality, because any time that you can reduce the amount of code you are better off. Just slow down and think about what you are doing. In the software world our schedules can be crazy and in the haste to get the code written and the application out the door we can cut short the parts of software development that actually lead to good applications.
Another thing you can do is to constantly look for code to refactor in order to shorten, simplify, or completely remove it. Constantly ask yourself if a piece of code needs to be there or not. Refactoring can be troublesome though, and if you do not have sufficient tests to check your refactorings then you may end up introducing more bugs than you are avoiding.
One last thing you can do is to avoid large or complex methods and classes. You may think that bugs are distributed evenly around an application, but that just isn't true. According to Steve McConnell one study found that "Eighty percent of the errors are found in 20 percent of a project's classes or routines" and another found that "Fifty percent of the errors are found in 5 percent of a project's classes". The more large and complex a method or routine is, the more likely it is to contain errors and the harder those errors will be to fix.