Patience is definetly the key. We have been married 30 years and I tried once we became empty nesters (about 15 -20 years ago) to spice it up ,offered her a hall pass, showed her swinger porn,etc. Took her to several bars and asked her to flirt with guys she found sexy, but was always met with, "I'm happy with what I got". or usually with a flatout NO. About 8 years ago she came home from the gym and was all bubbly and excited they hired a new trainer, he was in his 30's according to her and after a week or two told me she was going to switch trainers. I knew something was up so I went to the gym and met him. Very nice guy ,tall, well built, had a great personality so I saw what was making her school girlish, I decided to get to know him better and talk to him more in depth when we were comfortable with each other.
After a few months he and i decided to go out one night and have a drink. After the second drink I asked him if he found the wife attractive, him almost spitting out his drink, he admitted she was in extremely good shape for her age and easy on the eyes. The next question I asked was if he would be up to seducing her, that one I thought he was going to fall out of his chair. I explained how I wanted her to open up and enjoy sex more and I had asked her to go to bed with other men over the years. I explained I was on board but she was going to be the hard sell, that he couldn't pursue to hard or he would scare her off. We agreed to this and I left it up to him to try and get her in bed.
It took him about a year but he succeeded in getting her into his bed (that's another story) and on her trip home she got a case of the guilts. To make a long story short she and I had several days discussion about it, that I had influenced the setup and that I loved her to enjoy the attraction of other men. Her first was with us for about 5 years until he transferred out of state. She is now comfortable in the lifestyle and has been with 12 other men since her first. We and she especially enjoy the hot sex and attention paid to her and hopefully will continue on for a few more years