We've published a Getting Started guide for new Allura contributors at http://allura.sourceforge.net/docs/contributing.html. To accompany the guide, we've created a new 'bitesize' ticket label to identify open tickets that may be suitable for new contributors. Bitesize tickets can be found at https://sourceforge.net/p/allura/tickets/search/?q=labels%3Abitesize (link is also included in the docs).
If you're interested in contributing to Allura, don't be intimidated - jump in and we'll help you! -- Tim Van Steenburgh