The first to do is to get on the project mailing list.
Issue tracker can be used to report bugs and submit patches.
Request to join this project can be made here. Glassfish developers will be accepted without much fuss. Newcomers will need to partake in discussions and submit patches, before he/she can be nominated to be a developer, as is the usual practice in an open source project. It would be a good idea to send an email to introduce yourself when requesting to join the project.