Get to the the park gates 15-30 minutes before posted early entry. We got there at 7:50 and they had already opened the gates. Have tickets and room keys easily accessible, as you will have to show them. You will need the tickets first, then after you walk a little through the park, you will have to show your room keys (one for each person) to a TM before you enter Seuss Landing. Follow the crowd to Hogsmeade.
Ride FJ, then ride Flight of the Hippogriff, or check out Hogsmeade and grab a Butterbeer or Pumpkin Juice, or ride Dragon Challenge (if big coasters appeal to you). Or, if Ollivander's is important to you, get in line for that.
You may only have time to do 2 or 3 of the above in the first 45-50 minutes, then it will be time to get on the HE and ride it to Diagon Alley. Go straight to Gringotts and ride it, then check out all of the cool things in Diagon Alley. Don't miss Knockturn Alley. It is easy to miss, but it is really cool. If you missed something you wanted to do in Hogsmeade, ride the HE back to Hogsmeade and do it. (Hogwarts Express is a different ride from Diagon Alley to Hogsmeade than from Hogsmeade to Diagon Alley, so you should do both ways.) If you have to save something in Hogsmeade, I would save Dragon Challenge and Flight of the Hippogriff because you can use express passes with them.
I would say pick the most important things (and the ones without express passes) to you in Hogsmeade and do those first, then ride HE at about 8:45. We had three early entry days, so we did different things first each morning.