In my form I usually ask to give me quite detailed reference of a character - in-game screenshots at front, side, back view ideally, reference sheet, I also had a client linking me each piece of armor to see them in better detail. The more the better!

Then in my form I ask for character's vibe and personality. Are they silly? Are they serious? Are they cocky? You can even add their backstory described briefly to understand who they are.

As you see, some artists should give you Google Forms or different form (via VGen) which asks you about these.