Dress for the weather, which is always hot and humid. Wear comfortable shoes, a light-colored cap or hat, moisture-wicking socks and sunscreen. You will move slower if you don't dress appropriately. Bring a light backpack or carrying case for any souvenirs so you don't have to waste time buying one.
Be at the park at least 45 minutes before the gates open. The heavy crowds arrive within an hour after the gates open, so you need to get the jump on them.
Print a map of the park ahead of time and map out a schedule of what you want to do first, second, third and so forth. Work out a route to get to the attractions in order, and have every member of the group follow that schedule. Avoid Fantasyland in the daytime when it's filled with young children; try to visit during the parade.
Check the DisneyWorld site to see where the characters will be, then set up a plan to meet them. Have everything like cameras and autograph books ready to go before you meet the characters.
Take advantage of the in-park transportation. There are places where it is easier to walk than ride, but some bus routes can get you around the park faster than the monorail or the boats.
Use Fastpass when possible. If a line is too long, scan the ticket and get a Fastpass printout with a return time. Come back to the ride or attraction at the determined time. Disney World also has a feature called Extra Magic Hours for guests of any Disney hotel. Those guests can enter the park an hour early. See the DisneyWorld website for more information.