In my experience, there are no shortcuts. The approach is always fix some bugs, write some test coverage, and add some small features. Depending on the size o

In my experience, there are no shortcuts. The approach is always fix some bugs, write some test coverage, and add some small features. Depending on the size of the project, it might be quick or might take a long time. One problem you might face if the codebase is really old, are the multitude of styles and patterns that exist in different areas of the project. For those, it’s good to start in one area, and slowly reach out to other areas over time. --EDIT-- Thinking about this some more, here are some other tips: First and foremost - remember Chesterton's Fence. If you see something that looks strange and unnecessary - don't remove it, it might be load bearing! Also, if you are working in an IDE that has a step-through debugger (common in C#, Java, and others), then set an early breakpoint for an API call and follow it all the way down the rabbit hole...you'll see things happening that you never would have found by manually poking around source.