I've spent a lot of time creating supports and adapted games to help individuals with ASD with their social skills and interactions. The other day I was consulting with a teacher and she had a middle school student who was doing really well playing games, but having a really difficult time initiating play.
So we came up with a visual to help him, which is today's free autism resource. This social guide has supports to help with joining a game, inviting others to play, and some basic rules for all game. Review these with your student before engaging with peers, and then have the visual available throughout the encounter as a support. When you are first teaching how to use this visual, you can manufacture situations to help the student be successful, then generalize to more naturalistic settings.
Check out more supports for building social skills on our resources page!