Disney is expensive, so come prepared to spend lots of money on food, and if you're the souvenir lover, for those, too...
We (adults) have gone to Disney a lot, but now that we have kids (two of whom are adults for Disney's prices - over 10), it has gotten far more expensive for us, so we only go once every 2 to 3 years. It's best to get up and get to the park early. There's an opening show every morning. If you don't care to watch that, arrive about 10 minutes after opening to avoid most lines getting in.
Many new people start looking around right away. Repeat visitors head to some of the popular rides quickly. If you want to ride Dumbo, head there quickly, as that ride does not have a Fast Track line and the line will last forever later in the day. Check your park list for popular rides you want to do that don't have Fast Track. What you want to do first is based on your preferences, as there are many popular rides.
Fast Track is one of the best systems ever invented. It allows you to get a ticket, return to the ride within a timeframe (printed on the ticket), and then head to the front of the line with a 10-minute (usually less) wait time. You literally walk past everyone else who has been waiting forever. They could have done the same if they had chosen to. It is available for many of the popular rides and you should use it. That's what it's there for!
During the crowded midday, we head over to Tom Sawyer's Island and let the kids have the run of it. The hubby and I relax and explore - or enjoy the rocking chairs and people-watch. The kids meet us at the appointed time and we head back to the rest of the park.
If you can afford it, kids love eating at Cinderella's Castle, though you need priority seating to get in most of the time. (Call Disney's priority seating phone number in before your visit.)
During the parade times, lines can be shorter for rides - just be sure you are on the side of the parade route you want to be on. Watch the Electrical Parade at the end of the day - it's gorgeous. Also watch the Wishes fireworks show at night - it's REALLY nice!
If you're staying at Disney - any resort - shop midday, when the park is crowded, and have your packages sent to your room. In the evening, the gift shops are VERY crowded.
In general, service and cleanliness at Disney is second to none for theme parks - and it's THAT magic that makes it really special. Ask any employee any question and everyone is eager to please you - which is exactly what you want on vacation.