I've been to WDW 5 times,
Disneyland once and Tokyo Disneyland once with my 23 month old daughter.
(1) Bring your own stroller.
(2) Bring your own sippy cups, bottles, etc.
(3) Bring 2 days worth of diapers, wipes, baby food, formula (if used). Buy more at Publix when you get there.
(4) Take it at your baby's pace.
(5) Visit the Child Care Centers in the parks often.
(6) Bring a sling to keep the baby close when you go on rides. It also allows you to have 2 free hands and makes holding the baby while in line easier.
(7) "Baby swap" on the thrill rides so both adults can ride.
(8) Bring your own car seat if you're renting a car.
(9) Make at least one reservation for a character meal. The characters love babies.
(10) Have a great time!