Maintainability Guidelines

You are asking about good points about maintaining an asp.net application. The actual maintainability of an application is dependent on how it is designed and built. If that has failed, you can only salvage as good as you can.

Try to spot redundant code and make methods or classes for that. This will shorten the actual code that must be maintained and makes changes to specific functionality easier because it can be done by changing it only once.

But before you do any coding, familiarize yourself with the application and try to fully understand what it is meant to do. This makes it more easy to understand the code and understand hacks even though they are as ugly as hell. At this point, you just need to look beyond your own knowledge and try to understand the coding methods someone used by the one before you. Sometimes it will give insight about new methods and ways of coding. Most of the time it's just crying about the pore quality but with an occasional laugh about some ridiculous implementation. (I could make a site with some coding horror that goes beyond your, and also my, imagination.)

Good luck!

You are primarily going to be thinking about technical debt. You can find a good article with some decent links here[^].