I'm a fan of submodules in git, but sometimes it seems like I'm the only one! After having worked with this approach on a few projects, I'm coming to the conclusion that, like so many other things, it's easy when you know how! So, I tried to take my handwavy explanation of how to work with submodules, and turn it into a handy diagram for you ...

The basic premise is this: remember that you need to commit to both the parent project and the submodule - do the submodule first. You need to update the submodule when you update your main project. Stay away from git add . because it's alarmingly easy to revert submodule changes ... so simple really :)