Becoming familar with an open source project's code base can be quite overwhelming, especially for new developers.
In the past days, we went through our Jira bug tracker and tried to identify a number of relatively easy tasks that would be suitable for new developers to become familar with the code base and processes involved. We've collected them on a dedicated Wiki page titled Low hanging fruit tasks.
These should be fairly simple and isolated tasks, so they would be ideal for someone to dip his toes into the water.
If you're looking for something to hone your skills and expertise, these might be a good start. If you're interested on working on any of these, please let us know!