...which is in a similar vein to the things I swore I'd never do before I had children. It's quite embarrassing really.
Never feed the dog my leftovers. Particularly never let her lick my plate clean. 
No dog of mine would ever have free rein to jump on the sofa. God forbid she would ever sleep on my bed. Oops.
I would never let her do disgusting face licking kisses. (But she's just so cute when she does it).
She would only eat the highest quality food the fussy bugger will only eat Bakers, after much trial and error .
I'm sure there are more.