I just had a conversation with one of my previous contractors. I encouraged her to get involved with OSS. Her response was, "Haha, they don't want me." That made me pause and reflect about my own perceptions contributing to OSS. I know where she's coming from. I was there. I felt the same hesitation she did and I'm sure I'm not part of a minority here.
It's very daunting to jump into something so huge where the people involved are much more experienced and talented than we are. We all have to start somewhere though and this is what you could do if you feel hesitant about helping out in an open source project.
Newbies can help too
Add or update documentation
You may not know exactly what you can fix, but you're pretty familiar with a specific project. Help about by adding documentation, updating outdated material, or fixing grammar errors and typos. You may think it's a small contribution, but your small contribution helps the rest of the community that actually depend many times on documentation to ramp up quickly or for reference.
Using a project and found a bug? Report it. Be sure to include the exact steps you made 'til you encountered the bug. This will help other developers reproduce the problem and help them focus more on the problem instead of asking you boilerplate questions.
Include the exact environment where applicable: operating system and version, browser and version, programming language and server, etc.
Perhaps you have an idea about a feature you think other developers would benefit from. Report it. If you're on GitHub, just open up a new issue and add the details about your über-awesome feature. If there's a need for it, others will chime in and give their feedback.
Provide support for newcomers
You can contribute to the OSS community in the form of support. A couple of places that you could go to help is on the GitHub issues of your favorite project, IRC rooms, StackOverflow, Twitter, and by sharing what you've learned on your own blog or other writing outlet.
Yes, we need you
Think you couldn't help? Think again. You can help. Remember, it's so cliché but true: crawl before you run. Start small and eventually you'll get the hang of it. In the end you'll be helping others and yourself as well.