I’m sure everyone is different,but here is my 2 cents.
First you have to find another couple you are both physically attracted to. I don’t know how many times my lady and I looked at a couple and went “Oh,she’s cute,we could have some fun with her but her man is flat nasty.”. So you need to make sure both of you find both partners of the other couple attractive and acceptable
Next,you have to get to know them. Chat with them and discuss things you like and what you don’t like. My lady will give head,but I’m the only one allowed to cum in her mouth. You have to communicate things like that.
If you have never done any kind of activity like this,it might be a good idea to start with just same room sex. Then you can progress to just the girls playing together,soft swapping and then try full swap once you are comfortable