I am tinkering around with some simple Canvas based cave flyer game and I would like to make it multiplayer eventually. The plan is to use Node.js on the server side.

The data sent over would consists of position of each player, direction, velocity and such. The player movements are simple force physics, so I should be able to extrapolate movements before next update from server.

Any tips or best practices on the communications side? I guess web sockets are the way to go. Should I send information in every pass of the game loop or with specified intervals? Also, I don't mind if it doesn't work with older browsers.