Ok so boundaries gotta work both ways. Don't try anything that's going to harm your mate that bit is obvious. Understanding their body language so you know what they want and when they are telling you no. That's the other big thing with them.
On the flip side you've gotta set boundaries for when is and isn't a good time and place for sex. Basically you do this by showing them the appropriate places and letting them know that you're busy if they ask at inopportune times.