I've got 3 full days (+ nights) left for Luxor and Aswan.What's the best way to spend them?

E.g., should I fly to Luxor and do some sight-seeing, then trip on the Nile and then a little sightseeing at Aswan? I'm not aware of the time required for all these, and would like to get a -small- taste of everything. Any ideas how to go about it?Thanks!