What is the best method for multiple people to work on a game on quest?

there's lots of free/not-free 'versioning' software out there, such as github (free) --- if you can understand it (HK still has trouble with it), just google: versioning software

compartmentalize/specialize/divide/separate tasks (making library files):

one person works on combat
one person works on the world
etc etc etc

We did Pixie’s Quest together and, thanks to KV, we submitted pieces to github and he pieced them together. Ours was set up where each person had their own little world which probably made it easier than if you all chipped in and worked on where ever the previous author left off. I guess it depends on how you set it up. Once all was compiled, he submitted the game.

http://textadventures.co.uk/games/view/jymfhimg00c5cvrdqna7xa/pixies-quest

There is not an ideal way, but there are several possibilities. Another way is to set up a user that you can all log in to, and use the web version (as long as you are not working on the same room or object or whatever at the same time). The on-line version does have some restrictions.

HK's github method will work best if only one of you is doing it at a time, and then commits to the central repository, then the next person can take a turn. You can merge changes from two different people, but read up on how to do it before you go this route.

You could each create a library with your stuff in, but Quest cannot be used to edit library files, so you would be working in XML and code, which is far from ideal.

XanMag's method of each creating their own world is good as long as you have someone able to stitch them all together at the end. Again, make sure some can before you commit to it.