Don't go to a park on its' early entry day unless you are going for early entry. It seems to get very crowded on those days, so if you aren't an early riser, go somewhere else. Also, if you do go for early entry, leave the park when the gates open to everyone else and go somewhere else.
NEVER go to MK on Sat. night!!!
Epcot WS is so beautiful @ night and with the other parks closing so early anymore, it's nice to go there in the evening. Also, WS is soooo empty at its' opening (usually 11:00, I think) and that can be nice too, especially if you get a late start on your day or just want to take it easy, maybe have a nice lunch and go back to your hotel to nap or swim.
Since AK closes @ 5:00, you need to go there in the morning. Also the animals are more active then. Plan to go there on your coolest day, I don't know why but it always seems to be 10 degrees hotter in that park.
Go to MGM in the evening. See Fantasmic! It is a must if you've never been. Try to sit in the center and don't sit in front or you will get wet. If you've seen it before, you will be able to do other things easier because almost everyone who is in the park goes to the show.
Have a great trip