Be good to them. Understand their needs and wants. If you just bully them the whole time without any rewards or giving them any love then you'll genuinely destroy them emotionally.
It's fine to boss them around and pin them down, but consent is key. Have a safe word and reward them when they're good.
Tell them if they're doing something bad.
Remember that outside of a fetish you're dealing with an actual person. If they're on board with being called a pet and being totally submissive, they're practically giving themselves to you.
There's a lot of weight that comes with that. So don't fuck them up unless you genuinely are a sadist who wants to mentally harm a loved one.