How to convince your partner
First of all, it must be kept in mind that swinging is not for everyone. Before you try to convince your partner to swing you first need to look at yourself and ask yourself why you want to swing. If the only reason you want to swing is so that you can "get more action", then you shouldn't even bother. That is not what this lifestyle is about.
You must determine whether your partner can handle swinging, even if he or she is interested. If you want to swing because you want to help your partner live out fantasies while living out your own or because you want to share the most special part of your life (your partner) with others then you can start looking at how to convince your partner.
Your partner is no different then anyone else who would want to please you. If you ask them the same thing over and over again it won't be long before they give in and do what they can to try to accommodate your requests. If they are really not ready to swing you should not pressure them. That is why communication is so important in a relationship in this lifestyle. It could be really embarrassing if you attended a club and a hot couple wants to hook up with you two and one of you is an eager beaver and the other hates it. Sometimes a situation like this can cause more trouble then it's worth.
Many wives and girlfriends go to clubs for the sole purpose of pleasing their husbands or boyfriends. They don't particularly like the idea of swinging or even enjoy it. They basically give in just to keep the peace and to keep him happy. You should avoid a situation like this at all costs. Risking your relationship just isn't worth it.
If swinging is something that you both want to do you may not even need to convince your partner. They may already be more than willing -- all you have to do is let them know that you want to try it.
The first thing you need to do is talk about your fantasies. Yes talk! I cannot stress how very important it is to communicate with your partner. If they really love you they will listen. Be open to answer any question that they may bring up and be prepared to answer why you want to try swinging. Take your time -- it takes time to become comfortable with the whole idea. At one point you have to ask it, "What about if we give it a try?" If your partner is adamant and says "No Way!", then back off. Pushing them will get you nowhere and pressuring them to go will eventually destroy your relationship.
After some time you can mention your fantasies to him/her while talking some more about it. Maybe you can talk them into going just to watch at first and just to meet people. It may take several months, but if you can get your partner turned on you are moving in the right direction.
Don't forget, swinging won't fix a bad relationship, but it can make a good one that much better.