New "activities" in bed..

My boyfriend and I are in a long distance relationship and only see each other every 2-3 weeks. We have sex regularly and it's really good but lately he's been wanting me to try new things. He likes to talk dirty and be rough with me (which is sort of new stuff for us lately) by whenever he asks me to talk dirty or try something new, my mind goes completely blank and I can't think of anything besides stuff we've done before.

Any advice on stuff that I can say/do to turn up the heat?