The SitePoint Web blog has a recent post from Matthew Setter offering some helpful hints on working with other people's code. In it he shares suggestions ranging from the technical out to a bit more "learning oriented" to get up to speed on concepts and techniques.

Dealing with code created by other people is a fundamental skill for a developer. Give it a year and other people’s code could even be your own. Today I’m going to look at some of the best approaches for how to deal with other people’s code, read legacy code, effectively. It’s not an easy topic to cover.

He's broken it down into a list of several different topics, each with their own descriptions and links to tools or reading resources for more information:

• Interact
• Observe
• Run Tests
• Fix Bugs designed for Newcomers
• Find Available Resources
• Use a Good IDE
• Read Books & Blogs
• Contribute to Documentation
• Be Considerate

He puts some good emphasis on that final point, reminding the reader that it's not just years of experience that make for a better developer, it's more about skill.