I think starting your own open source project works to better improve your programming skills that contributing to existing open source projects.
Existing projects already have most of the code already written. A typical open source changeset is maybe 3 +'s and 5 -'s. Mostly contributing to open source projects will improve your people/communication skills because most of that you'll do it is talking to existing developers to understand the problem/how to debug the problem.
Existing projects already have most of the code already written. A typical open source changeset is maybe 3 +'s and 5 -'s. Mostly contributing to open source projects will improve your people/communication skills because most of that you'll do it is talking to existing developers to understand the problem/how to debug the problem.