Recently we added a new development method to our inventory: ScrIMP. It is derived from Scrum, an agile software development method and especially adapted to open source projects with ever changing team members.
The heart is frequent definition and reflection on short term goals as well as the implementation of these goals during defined short periods of time. For us this means that we offer the possibility to do a Sprint, i.e. to achieve a goal within 7 days (starting on fridays always). There is a place for volunteering, for progress reports and for reviewing.
Of course this is completely optional. Everybody can just contribute in his/her own preferred way. However we also hope to increase the attraction to new supporters.