If it is an informal shoot, such as a family shoot, ideally, you should talk to your client and recommend having the photoshoot in the rain; it will be a great adventure, and it will make for great photos. However, this may not be possible all the time owing to your or the client's circumstances.
So, if it is raining on the day of the shoot and it is an outdoor shoot, you can ask the client to reschedule the shoot with you.
In a rare case, if the client is or you are not able to reschedule the photoshoot, please contact us, and we will find a resolution.