I always start with a chat with my client, I put all the questions I need to know before I get started (like what style do they like, if they want to know more about the process while I do it, we set up the color pallete, I send them the moodboard I create in order for a better view on the illustration they need) and then I always keep in touch with them while doing the project in order to know if they want something to add or not.