Keep in mind that I've only been to WDW in the months of March, April and July. Mainly July.
Stay away from the Magic Kingdom from 2-4 in the afternoon if you plan to be on the rides. During that time a daily parade takes place called, "Share A Dream Come True". If you want to watch the parade, get to the Magic Kingdom around 1 and pick your spot to watch. You'll want a spot along Main Street because trying to leave Frontierland after the parade will be nothing but sheer horror! lol.
I forgot what time it was and headed over to the Magic Kingdom a couple years ago to tape it. I went through Tomorrowland first and finally made my way over to Frontierland, now, as I was alone it wasn't difficult to stay with a family or friends or something like that...but I literally, LITERALLY had to squeeze between people I didn't even know in order to get out. I couldn't see where I was going as I was not the tallest person around, heh...I just thanked my lucky stars that I know the MK like the back of my hand.
The best time to visit the parks is during or after a rain storm. Just have your ponchos with you. (They can fold up REAL small. I was able to get my fairly large poncho in my fairly small fanny pack *yes I know, I wear a fanny pack...lol*) When we were at MGM, the rain poured and the park cleared up. We got onto Rock 'N' Roller Coaster 4 times in a row without more than a 2 minute wait, plus the pre-show. We could have gone more, but had other things to get done...including reuniting with our family, lol.
Chose what park you want to get done a day and get there for opening, then, get to the ride you want to do. That is important (at least it is for us in July...yet, that is also a very crowded month).
Bring water and lots of it. You need to stay hydrated and the bottled water is expensive...and the Floridian water is just disgusting lol.
You have to eat at Casey's Corner at the MK! lol. It is a counter service restaurant, but the theme is really cute! It's themed after the poem "Casey At The Bat" and so it's baseball. The serve hot dogs and the famous Grand Slam Hot Dog! You can also eat outside and listen to the Main Street pianist play ragtime tunes! It's amazing to watch him play!! It really is.
Many people think Animal Kingdom is like a zoo...that is said out of pure ignorance to the park. When you see it you will know what I mean. The Animal Kingdom is FAR from being a zoo. There are no cages and the Kilamajaro Safari is amazing. The animals rome free among the vast lands and there have been times where the Safaris car had to stop to allow giraffes to cross. It's awesome.
Watch out for the actors and actresses on the streets of MGM! They are hilarious and if you are present when they are around...you might just be included in their lives...heh.
Fast Passes will become your best friend, lol. Take advantage of them!!!! They are free and available...USE THEM! heh.
Take a look at some of the other resorts! You get a better look at them in real life than online and if you are considering on going to WDW again, you'll know what they are like.
Get up early and stay out late! lol You're going to WDW so don't expect to relax!

Trust me, you'll want to get the MOST out of WDW and that will require LONG days.
You will want to watch Wishes, but not every night. Fantasmic is also a fun show, but you will need to get there close to two hours early for a good seat. That place fills FAST!
These are some rides that will probably "mostly" require Fast Passes (during a sunny day):
Splash Mountain
Big Thunder Mountain
Soarin'
Test Track (the singles line is actually the better way to go if you don't mind risking the chance of not sitting next to your family)
Mission: Space (again, the singles line is good)
Tower of Terror
Rock 'n' Roller Coaster
Peter Pan's Flight
..and most of the Fantasyland attractions
Kali River Rapids (considering when you're going, you might not need one for this ride)
Take advantage of the EMH. The crowds may not be much of a change from the day, but if you're willing to spend the day at that park, why not spend a few extra hours there! Remember...Get the MOST out of everything!!! When you are back at home you will want to think back and know you really did so much! Also, the memories are priceless...so create them!!
Take pictures with characters!!!! No matter how old you are, it's either, cute, funny, nice, or just so awesome to look at pictures with yourself, friends or family with characters!
Besides character pictures, just take AS MANY pictures as you can!!! When you get back home you will have a BLAST looking at them.
Take a good look at the things around you. While you will not be able to see everything, there are many small, "hidden" surprises around the parks! Such as hidden mickeys.
Buy things as you see them!! You will probably see things and say to yourself, "nah, I'll buy it later", and then you never buy it again or you don't see it again. Thenm when you get home you're kicking yourself for not buying it. Souveniers are awesome and help ease your mind when you are leaving WDW.
If you are such a WDW fan and if you REALLY enjoyed WDW, you have to be prepared to feel a bit saddend when you are going home. I don't mean to sound horrible, but I just thought I'd warn you. When you are feeling a bit depressed, just remember what you are going home to! The rest of your family, your house, your own bed and all the little things you didn't have down at WDW. With the pictures, souveniers and memories of WDW, it won't be so difficult...so TAKE PICTURES!
Also, it's a good idea to bring a journal. At the end of each day just write what happened, what your best moments were and what you thought was the highlight of each day. Write were you ate and some things that stood out to you. You will have SOOOOO much fun reading it once you return home. And the best part is, you'll have EVEN MORE fun reading it after a large time passes by.
It's good to bring a couple different swim suits. If you plan on using the pools often. While one is wet, it might be more comfortable to slip into a dry one if you plan on swimming again that day.
Also, bring a nice outfit. With a nice outfit with you, you don't have to hold back on going to the nice restaurants...even if you don't plan on going to one, it will be nice to have a nice outfit if you change your mind.
Keep in mind the restaurants that require a dress code.
Victoria and Albert's is the most strict on this rule. Women wear dresses or a formal suit and the men wear a formal suit with a jacket and a tie.
Citrico's is a sort of semi-formal to business casual. Don't wear flip flops there or other inappropriate sandals.
The nicer restaurants are found in the resorts...however, there are plenty of nice ones around the parks as well.
If you are looking for a fun, family-style place to eat...try 50's Prime Time. Both parents and kids become kids and the waiters and waitresses are your mothers and fathers. Make sure to keep your elbows off the table and don't forget to set the table!! Oh...and remember to eat your vegitables!!!
VMK Central at WDW sucks. (for lack of better word...haha). Some of the keyboards don't have letters on the, so make sure you know your keyboard by heart! heh. Also, the mouse is a little ball so it might be difficult to use at first. The keys are hard to press down at times as well. Make sure to print out the downloadable quests from online and bring them to WDW. The Thrill Seeker's quest will need to be stamped at Kali River Rapids in Animal Kingdom.
I could go on and on about WDW. If you have any specific questions, just ask! I would be more than happy to answer...trust me lol.