The process itself is fairly self-explanatory when you open Google Forms! You have full control over how you wanna design it, and it really depends on the types of commissions you offer. I like to make the description a brief version of my TOS (like how many revisions are included etc.) and then keep the questions short and sweet and all on one page so people know what they're getting into without getting too overwhelmed. If you offer multiple styles or types of illustrations in the same form, I highly recommend adding pictures for clarity (and because that makes it look nice lol) - you can also add the price in a short description underneath. Make the important fields required (name, email, style/type of commission, character reference), and have at least one optional one for additional comments if needed.
For some other general tips, I'd suggest taking some time to look at all the settings and not require anyone responding to be logged in to a Google account (but do make a field asking for an email address so you can contact/invoice them lol). You'll also want to double-check if all the fields work as intended since depending on the type you choose, they'll have different properties: if you make an email field, it will NEED an email, so make sure you don't accidentally use it where you want someone to paste a link or write a description of their request. It helps to have a friend try filling the form to see if it's clear and functional.
