It Takes Two to Shower — this could be the name of a book about this experience. Having shower together can be a pleasant experience by itself or a foreplay.
Lather up and stroke each other carefully but provocatively. You can caress each other’s genitals a little. Use silicone based lubricant. Shower gel and soap are not suitable — they can cause irritation.
If you wish, continue the petting in the bedroom or other rooms.