Most important things to learn:
* React-JS for the UI development
* API to construct proper documentation
Besides that you can also help with alot of little things like
* translations of the GUI (if you speak a second language)
* tech support in the forums
* education on bitcoin meetups (if you feel fit for that)
What's your expertise?
//i just realized this is in peertracks .. so not sure my answer is qualified. Sorry