I do modern dancing and my teacher asked me to lead the warm-up / stretch for the other students before class starts. I know that individuals have different needs and should probably have specialized exercises, but are there general things I could let them do? Something that could benefit everyone without causing injury?
I danced for a long time and have a BA in it and was part of a modern dance company. I would look at really some general yoga stretching to begin with, this is something that we always did. A big key is to make sure you get the blood moving first to avoid injury. A simple way is to just make the class do jumping jacks, but that is boring. Since its modern dance, some more "dancy" warm ups might be more interesting. Contact improv, improv across the floor, basic movement, etc. Just get a little bit of a sweat up. You probably have done plenty of stretches in the past, so focus on the muscles you are intending to use when dancing, this would be obviously the legs, lower back, upper back, abs, hips, etc. We used to do lots of hollow body and rolling movements as well to increase mobility.
Sorry if i rambled a little bit but i hope this helps. I'd say the yoga stuff is key if you are looking not to worry about injury since everyone can go at their own pace.