There are many things that I don't like and I will never draw them. If you want me to draw something for you, please keep all these 'rules' in mind (no matter is it a commission or a trade, etc).
I only draw characters, such as fursonas, OCs, fan characters, etc. I never draw real people and animals (such as your irl cat pet, for example). I don't draw abstract art and landscapes (I can draw them as a background though).
I don't draw anything that is illegal or is against the rules (of Weasyl, DeviantART and FurAffinity). I don't draw anything that features and/or promotes any kind of hate. I don't draw anything that features any political or religious themes.
I will never draw my characters in any scenarios that I don't like.
Basically I can draw anything that is totally clean, SFW and family-friendly (as long as it's following all of those rules above).