Do not start anything with a baby/young child that you’re not willing to continue for 18 years.
For me, that was rocking a child. I don’t like doing it. So I never rocked babies. I held them, I walked with them (ah, for those days when my knee didn’t hurt!)–but I didn’t rock them. Turned out to be a good thing–no rocking chairs in ice skating rinks!
Seriously, it’s a good rule. E.g., if you don’t want your child to become a TV addict–don’t let them watch TV non-stop when they’re babies/toddlers–ever, even when someone is sick.
If you don’t want to sing all the verses of a long song at bedtime, don’t start it. Pick a short little song instead.
If you don’t want your kids to eat junk, don’t feed it to them, ever. I personally think this one will fall by the wayside if the child ever spends any time with anyone else besides Mom and Dad–junk food is so tasty! But at least at home, if you want your children to be junk-food free, you can just never start it with toddlers.