the usual idea with Abu Simbel is to arrive just before dawn. When I did it that involved a 2am start, to fly there; people who went by coach left earlier but didn't actually arrive till the sun was already up. But actually, dawn isn't all that magical, so over to you whether you fly or not. Either way, it is worth seeing.
In Luxor you'd normally visit the Valley of the Kings (probably going into a couple of tombs) and perhaps Hatshepsut's temple, which is nearby. Colossi are on the way there. (None of these is far away, only a couple of miles at the most, I think.) Luxor temple - right in town - and Karnak, a few miles further away, are generally two separate trips; you might want to do only one if you're feeling bushed. (Karnak is better, Luxor is closer.)
Cruises are generally from Luxor to Aswan, and maybe back again (or the other way round). Aswan's not got so many old things to see - the dam's just a dam; but a felucca to the island in the middle of the river is nice.