If you are thinking of doing this so you can screw other women, or watch some guy have sex with your partner, you maybe doing this for the wrong reasons.
My wife and I have been sharing partners for over 20 years. We have sex on a regular basis with 2 other couples. The six of us have had a great time together for many years. These are incredibly intimate relationships and we find them very rewarding. To us it is more about the relationships we have with the other couples and not about the sex; don't get me wrong, the sex is terrific.
The six of us have 3 tenets that we like to follow...
Respect and Pleasure your partners.
Remember your biggest sex organ is your brain, keep it engaged.
Enjoy the moment, enjoy your partners, and enjoy the sex.