first sploshing advice please

I have been sploshing by myself for a few years but my gf has said that she will give it a try with me some time. We have already discussed it a bit and will be just custard and only in underwear or less. The problem is.I don't really know how to do this with another person to make sure she feels comfortable and enjoys it and hopefully wants to do it again. Please can i have any advice or pointers to help me make sure she enjoys it as much As I know I will.
Thank you
Thank you