Some thoughts....
If the camera is in the bag, you're going to miss the moment. You're going to miss your child/wife/girlfriend/goldfish/"service animal" doing that horribly cute thing in front of you and by the time you get the camera out of the bag, its long gone. Keep it on your shoulder.
Learn How to Use your Camera. If you don't know how to use your camera at home, there's no way you're going to learn exactly how it works in a 5 day vacation at Disney/Universal/Sea World/Jamaica/San Quention.
*When all else fails, Green Box. If you didn't take the last bit of advice, just stick your fancy camera on the green box mode (AKA Idiot Mode) and use that. It will produce a usable image without you having put any thought into what you're doing.
Learn how the Flash Works! The pop up flash on your camera will likely go 10 feet. Its great for fill flash in bright sunlight to fill in the shadows in someone's face. Great on MSUSA as the light is either overhead or coming from the west/left. Your flash will be rather useless during the Electrical Parade; instead boost the ISO and photograph the parade how the designers intended it.
Make your Subject Big in the frame. So you want to pose your family in front of Cinderellas Castle/SSE/Haunted Mansion/Godzilla. Instead of having them stand directly underneath or immediately in front of the background element, have them stand about 5 feet from the camera. This serves two purposes: 1 - Your loved one is not some tiny dot in the background. 2 - you're not waiting forever for a clear shot of 50 feet to try and shoot in with a theme park of 47,000 other people.
Its okay to cut off their feet! Waist up composition is fine, we dont always need to see head to toe. Faces are whats important, not whats two feet off the ground. (Unless you are traveling with Peter Dinkledge)
Get down on your kids level! Don't look down at your children. Get down on your knees at ground level when youre photographing them. (*Advil not included)
Anticipate! Look, you know your kids/wife/pets better than anyone. By now you probably can predict what cute thing theyre going to do. Anticipate what they're going to do and be ready for that moment.
Forget Haunted Mansion. Look, There's a handful of people who can get anything usable off that ride. We either have spent way too much money on very high end lenses (24/1.4) & dSLRs (5dMk3) or had the ride E-stop in a very fortuitous place (like in front of the cemetery guy & his dog). If you havent made a sizable investment, just come back at night and make a photo outside. You will frustrate yourself.
Disney has people in them, Your Photos should too. An empty Disney World is just creepy. People give Disney the magic that makes this place, waiting to photograph a building with no one in front of it seems rather pointless IMO.
Be Original! If you're with a group of you and your friends & everyone is shooting, Get something different from them. No one wants the exact same photo as the person next to you. Which leads us to....
Shoot Wide! Give me Context! Just because you have a 70-200 or a telephoto lens doesnt mean you should always use it. WDW is a beautiful place, full of flowers and interesting design features. Find ways to incorporate them in the photos. Dont just automatically zoom in and shoot a tight face shot. However that leads us to.....
Use what you've got on the camera! Trying to change a lens to capture a moment is very hard to do. Unless you see whats likely to happen, be able to reach into a bag, change a lens and get into position with 5-10 seconds, stick with whatever lens you have on the camera. Capturing the moment with an imperfect lens beats missing it entirely.
Dont be gimicky! Stop using that fisheye. Stop tilting the horizon. Stop oversaturating. Stop shooting for HDR. These are all gimmicks. None of them are good. You will be made fun of accordingly.... as I am here. Learn good composition and recognizing good light instead.
Your iPad is not a Camera! Stop. Just stop it. You look ridiculous holding up your cookie sheet and you're blocking people behind you. They will yell at you. They will heckle you. They will just take your photo & put it online. You will be made fun of accordingly... as I am here. Leading into....
Social Media? You want to be able to Instagram/facebook/twitter it moments afterwards? Shoot with an
eye-fi card & upload them to your tablet/iPhone/Android device. Much more cost effective, plus you spent a lot of money on that fancy camera, use it! I love my iPhone's camera as much as the next person but trying to get the same image on your camera and your phone is insanely difficult. I did this throughout SWW with great results.
Film Still Exists! So you completely forgot your camera. You dont have a camera phone. Disney still sells disposable film cameras, go buy one and get creative with it. You'll be surprised with how good you end up doing.
Be Subtle. Dont be obvious, instead blend in. Other guests came to WDW and theyre not here to watch you take photos. This means not carrying around a billion pounds of camera gear. It means not lining up six tripods with you and your friends across MSUSA. If you have a 300/2.8, it means not bringing in into the park. (Security & Managers
will have a talk with you if you do that) Your photos are not worth ruining someone else's experience. Which leads us to the most important thing.....
Have Fun. At the end of the day, its about capturing memories and having fun with your families/friends/gerbils. Dont sweat the little stuff, have fun making photos.