First, watch some MMF threesome porn. Any kind of porn can be an inspiration and courage. Tinder for threesomes porn can provide you with ideas about skills, threesome positions, possibilities and even creation. Porn can also be a huge turn on and it can ease your guard. When everyone is in the mood for a licentious party, things can get easier and bolder.
Clear boundaries. You might find each other on tinder for threesome dating apps or just a bars or clubs. No matter how you meet each other, it is necessary to have a conversation before doing business. You can communicate person to person or online chatting. So long as you are setting boundaries and clearing it with each other. MMF threesome boundaries can be a lot more than FFM threesomes, because it is already not easy for two straight men being naked in front of each other, let alone having sexual contact. Setting boundaries can save you from plenty of awkwardness.
Be open. If you think you just crossed a limit of yourself, don't be alarmed. Under such passionate and hot circumstance, many unexpected things can happen. You might think you will ever let another man to such your penis, but when it really happens, it may not feel so bad. Don't be surprised by yourself or by any other people. Just be open as much as possible. You will get to know yourself a lot more.
You can be the audience or let the other guy to be the audience if it is okay with him. Threesome does not always mean all three persons must be together and making love to each other. If it is too much for you to be sexually involved with another man, you can step back and watch them by the side. You can also be the star and play a show for the third man with the woman.
At that moment, any kind of threesome should be an exciting experience. Therefore, try to enjoy every minute of it. After all, you don't know when it will happen again or never.