I did a quick brain dump of some things that newbies can work on in:
http://wiki.quantlib.org/twiki/bin/view/Quantlib/NewbieProjectsThat page is editable so that people can add on their own ideas.
In particular, adding a new pricing engine and/or writing a unit tests is a
way that someone without much experience in the code can start and get
something quickly useful done without too much time commitment. Once you are
in the code, you'll probably find more things that you'd like to work on.
Some of the things I put on the list aren't coding related.
Generally, the development mode is to find something that you are interested
in or that you need done for internal use, and then let people know that you
are working on it so that people aren't reinventing the wheel.
Let me know if you need any help in getting started.