I'm not sure how to tell you how to work your way into the act of your wife being "fuck-licked" since that probably varies greatly from wife to wife. If my late wife is an example, I can assure you that you won't have to talk her into it the second time. So, if this is her fantasy, talk to her a lot. Explore ideas. Keep your eyes open for partners. We preferred couples but beware! You will have two women who won't have to be talked into it the second time.
After we found that magic couple, Laura and I (and the other couple) found the following description worked best.
A couch works better than a bed. Start with the women sitting on the couch with the men kneeling between their legs. Don't get in a hurry. Laura liked to have me start at the bottom of her slit, using my tongue to gently spread the labia sideways, slowing working myself up until the labia was spread widely along the length and above her clit, which would be standing erect and anxious. After the ladies have had enough of this (may take awhile) both of the men should sit on the couch and lean comfortably back while the ladies climb aboard.
Laura liked to start out face to face with her chosen fucker. (She liked kissing.) Eventually, the fuckee-lickee would turn around into reverse cowgirl position and reinsert the fucker's penis. Both would spread their legs and the licker would kneel between them. I've never questioned my sexuality so I wasn't put off by working around my friend's penis to (once again) spread the labia away with my tongue until her clit was once again standing firm at the top, easily licked.
One challenge to look out for at this stage is that the fucker's cock tends to slip out when the action becomes enthusiastic. This can be avoided by the licker pursing his lips and tongue around the clit while using his chin to hold the fucker's cock in place.
The lady who is not "It" can amuse herself by alternately kissing the fucker and the lady who is "It."
After a sufficient number of orgasms, which varies with individuals, the other lady can become "It" and the fucker and licker can exchange assignments.
One very pleasant variation is for one of the ladies to be the licker. Laura was fond of this as well because, at the proper time, she could help herself to a treat of man-cream.
Keep experimenting and report back to this forum.