One of the barriers to convert users into contributors in an open-source projects is that many people have no idea where to start. They are usually scared to take on large tasks because they are not comfortable enough with the code-base. Yet I think there are ways you can help them as a project maintainer.
One good way that I found to fix this is to tag specific issues that are a good starting point for new contributors. However I think the practice would be even more effective if more projects did the same way, so that people know to look for it.
I actually just noticed this labels on the Composer repository in the last week. Kinda surprised I hadn't noticed them earlier. When I asked him about them he said they had been there for quite some time. D'oh.
Great to see this post helping to spread the word.