Thanks for your question. First of all, does your wife trust you 100%. Do you have her heart, mind, and body in your control? A lady has to be 100% convinced you are love her and she trusts you no matter what. I ask this because this gives the swinging lifestyle a higher chance of growing than breaking you two up.
Back to the oringinal question. Ask her, how she feels about her sexual feelings and body. Ask her if she has any sexual fantasies and to share them with you. Discuss them in detail and show real interest. REMEMBER this is a 2 way street!!! Then she will see you enjoy listening to her mind and open up more to you. Then ask her about swinging and which websites you have been researching. Voila!!! go from there