This is when we always go. We're from Texas, and the weather at WDW is identical to ours here at home. This year we'll be there 7/5-13. It's going to be very hot and humid. Make sure you ware a wide brim hat and have plenty of sun screen. I don't know where your from or the weather you are use to, but this kind of weather combination can sap your energy very quickly if you don't learn to pace yourself. The best advice I can give you is drink water, drink water, and more water. Stay hydrated! I've seen many a person, adults and children, that forget to drink fluids, not cokes, and end up looking and felling bad, and ruining their vacation. If you quit sweating or felling bad, head to the first aid stations in the park. If your staying on property, take those afternoon breaks. Nap, go to the pool, relax. Then in the evening, come back and the crowds will have lessened greatly. Use the fastpass system! Don't try and see everthing, because you won't. Pick rides, shows places to eat that you want. Enjoy your vacation and don't become a commando set for a mission. It will rain somewhere at Disney during you stay, maybe where you are or not. It probably won't last long, but beware of the lightening storms they are serious stuff!
Have a great time!