One of the biggest "secrets" I know is to not buy bottle water. Most of the quick service locations have filtered water. Ask for a cup of ice water instead of spending $3 every time you are thirsty.
When trying to enter/exit Magic Kingdom, instead of walking through crowded Main St and dodging everyone stopping to take a picture of the castle, walk throught the gift shops. It can be troublesome if you have a stroller, but other than that it's usually a lot faster, not to mentioned it's air conditioned.
When buying snacks (this mostly works for families of 4 or more), it's better to buy one cupcake and cut it in 4 pieces. No one really needs to eat an entire giant cupcake on their own, and it's easier on the wallet.
Character Palooza is an amazing way to meet upwards of 8 characters in an incredibly short amount of time. Character Palooza happens at the exit of Tower of Terror (Kenny the Pirate has a schedule for specific times on specific dates). My girlfriend and I did Character Palooza three times when we went this past Feb. We met some pretty rare characters; Genie, Robin Hood, Evil Queen, and Pinocchio to name a few! If there is more than one Character Palooza a day, the characters usually don't change. With that being said, typically there are new characters every day! There were a couple characters that were there every time we went though (Tiana, Stitch, Jasmin, Aladdin).
PM me if you want any park specific secrets though!
EDIT: Seems like about a week after my original post, Disney World decided to "do away" with Character Palooza. Instead it will be a much more random event. See the below link for more details:
http://www.kennythepirate.com/2015/05/13/what-is-going-on-with-character-palooza/
