You don't need to join an open source project to improve your skills, you just need to practice, practice, and practice some more. You can pick an open source project that interests you, download the code and then work on finding and fixing bugs, or writing enhancements to the project without being part of it. When you succeed at doing something productive with the project you can submit the updates you have made to members of the project and perhaps become an active member of the project going forward. The key is that in order to learn, you have to get into code and break things, understand why you broke it, and learn how to fix it properly. No one learns without breaking something. Cheers and good luck to you.
I wasn't, now I am, then I won't be anymore.
