1. Keep dog still.. no running/moving/jumping a week after spay/neuter.
I didn't have Levi when he was neutered, but I can imagine that keeping such a wild little man still for a week was impossible!
2. Do not switch foods right away! You don't want to shock their stomachs.
I try, but I don't switch his food often. When we switched from Blue Buffalo to Orijen, I did gradually phase out his old food.
3. Never lets your dog sleep on the bed with you/play tug/etc..
HA! Levi always sleeps with me. And we play tug-of-war every day. Sometimes I even let him steal my socks and pretend like they are toys.
4. Don't let your dog walk ahead of you on walks
Levi almost always walks in front of me. He generally doesn't pull, so it's fine. I like for him to be in front - easier to keep an eye on him!
5. Never use a flexi!
We love our Flexi.

If we are in a situation in which it is inappropriate for Levi to use the full length of the Flexi, I just lock it in a short position. No big deal.
6. Don't give your dog junk food
I generally try not to give him junk, but I also try not to eat junk. I am guilty of giving him the occasional bite of a French fry, but that happens maybe once every few months. He gets plenty of good, healthy treats, like green beans or carrots. As far as junk dog food - no way. I'll occasionally mix in a bit of wet healthy food (like Wellness Core) into his kibble as a treat.
7. Do not BABY or spoil your dog!
Levi is extremely spoiled. My mom frequently uses the word "rotten" to describe him. As far as "babying," I try not to. I'd rather let him walk then carry him around. He's small, but he is very much a "real dog."
8. Let your dog adjust for a week before bringing people over to meet him/her as a puppy.
I didn't have him as a puppy. But he is very well socialized and has always been fine meeting friends/family members in mass numbers.
9. Don't encourage bad behavior.. no matter what.
I do try to correct his bad behavior. He does occasionally "steal" my stuff (like my socks!) which doesn't bother me, so I don't correct it.
10. Do not leave your dog alone with kids/other dogs alone.
When we visit my best friend, Levi always stays out with her chihuahua. They are the best of friends. I'm also comfortable leaving Levi out with some other dogs (my older brother's small dog, my aunt's two small dogs, etc). Levi is very familiar with all of the dogs I would consider leaving him alone with.
11. ALWAYS pick up your dogs poop.
In public, yes. At home, no.