Eye contact definitely.

My fiance and I are in a LDR. The night before we were going to make love for the first time, he IM'd me on line and said, "There is one thing I want you to do for me; I want you to keep your eyes open and look into mine when you come." I replied that I didn't know if I could do that, because it would make me feel like he was looking into my soul. He said, "I know. That's why I want you to do it." I thought it was the most erotic thing anyone had ever said or asked of me. It did make for a very powerful experience. Now when we're apart and I masturbate, I'll usually shut my eyes as I fantasize, but when I start to come, I always turn to his photo on the wall and look into his eyes. It just seems to make the orgasm stronger and makes me feel like we're sharing one all over again.

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Communication is the key.