It can be daunting to interact with other deer! Although I don't have social anxiety, what I do to "warm up" when playing in the Forest is to start interacting with Nameless since they're less likely to be an experienced player, and then go onto fawns.
Playing and interacting with fawns and Nameless is not only fun, but the new players (or new characters!) get some experience with the Forest body language, along with you, so everybody benefits C:

Your deer is more than welcome to interact with mine! I'm mostly on Haroten and Emmy, so feel free to pop on over and say hello. If they're sitting down, I may be tabbed out of the Forest doing something else, so don't fret if that happens.

I don't know what to do sometimes as well. The forest body language can only let you talk so much.
When I meet a group of deer, I usually don't hang back, but I don't bounce around and possibly annoy them. I bow as a greeting a lot of times, and then nod, tilt my head, dance, or rear up whenever I think I need to. Body language gets simpler as you go along, and because I admittedly roleplay my deer with a voice and everything, I can imagine an entire conversation, though it can be choppy.