We go every August. In fact, I've never not been during the summer. I'm from Ottawa, so we get the humidity (except this year summer hasn't started yet), but it's still hot. As someone said in an earlier post, summer = heat. Keeping that in mind, we always have an amazing time! Just follow some basic summer rules and you'll have the trip of a lifetime!
1. Rope drop. Seriously, rope drop. Not a morning person? Tough, now you are. Rope drop. It will still be hot at 8:15 ( yes, get there by 8:15), but you'll get to do the headliners and the other rides will be walk on. This is important as the more you do in the first 2 hours, the less planning and more relax time you have later on in the day.
2. Mid-afternoon break. You will hear from both sides of the camp on this issue, but in the summer, it's extremely beneficial. We like to book a sit down lunch, plan our afternoon/evening ( based on what was accomplished in the am), then go and swim/nap for about 2 1/2 hours at the resort. This really helps break up the day. Then back to the park or hop to a new one that evening.
3. Drink lots of water and go with the flow. Stay hydrated and let your plans fall apart if need be. Colortopia was an hour detour last year, and 1 day we swam and slept longer, but it was needed.
As for the rest, I do frog togs, my wife doesn't. Dole whips cure almost anything, and book your next fastpass right after your 3rd is finished. Smile at everyone, wish those with birthday buttons happy birthday, and pinch yourself every now and then, because you're at Disney!