The most important thing is to be on the lookout for spaghetti code (or other big chunks of hard-to-maintain code), and do something against it. There's lots o

The most important thing is to be on the lookout for spaghetti code (or other big chunks of hard-to-maintain code), and do something against it. There's lots of materials on how to refactor code (improving its structure without changing functionality), including blogs, books and video lectures.