I haven't done a game jam before.
What are the rules/etiquette about doing work before the actual jam period?
I'm probably going to get an environment set up implementing the constraints in advance, but I guess doing much more than that would probably be too much?
yes pretty much see that you have a working pipeline to draw stuff on screen, if your not to fermiliar with the engine your using try making a simple pong (or snake clone) to see everything is working just something to check the display functions, sound and inputs. little helper functions I would also still consider if there generic enugh like printing text, drawing shapes, or key rebinding and screen scale options. this would be the maximum amount you could do in my opinion.
This is a good answer! Your core game should be made from start to finish only in the allotted time. As long as you’re not doing more than someone starting fresh using a full game engine (game maker, unity) you should be fine. Like jeana says definitely take some time to familiarize yourself with whatever engine you’re using before the jam starts so you’re not going in blind! Good luck and feel free to ask as many questions as you need!