You can use the Visual Studio Debugger to unit test your methods as you are coding. When you complete a block or section of code, place a break point at the beginning of the block, then run the ASP.NET web application in debug mode and try to generate events that exhaust the various code paths/conditions. This way you can quickly validate that your code is behaving as expected and reduce bugs in the long run. This is a more proactive way of using the debugger but works quite well and is super easy to do.
For practice and more information about the debugger go to: http://www.csharpuniversity.com/2008/11/23/using-the-visual-web-developer-debugger/