Advice or tips?

My SO and i were talking last night and threesomes were brought up. I told him id consider it if we found someone who i knew wouldnt try to get with him after and that i wouldnt feel jealous about. Im also curious myself. His birthday is coming up and id like to maybe do it for his day. Tips or advice for making it a good night for him? I dont want to hear how its a bad idea or how others couldnt go for their man having sex with another female. Were both in agreement that it would be something to spice up our sex life as well. Ive never really thought about 3somes and how id go about having one.