I can tell you what worked for me.
When I first met my future wife, she told me that she wanted a swinging relationship or at least a relationship with an open minded man.
After we were married, I told her of my cuckold desires and we decided to take small steps to see how it goes and how we both feel. At first, she just gave a black guy a hand job while I watched. It was enjoyable for both of us so we went further and further over the course of the next ten meetings. That was 8 years ago and she currently has 3 black boyfriends who come over and fuck her on a regular basis while I watch. It's a great lifestyle and we both enjoy it.
My advice is to go slow and take small steps. Don't just have some guy jump on your wife and start fucking her. Start with a massage and/or handjob. Have her put on some lingerie, turn down the light, put on some music and let her massage him and stroke his cock. Then the next time, have her kiss his cock, suck it a little, etc. Work up to full on fucking over a course of a couple months or so.
That is absolutely the best way to ease into this lifestyle and test the waters. You can stop or continue at any time.