The key to visiting Angkor is to not try to do too much. As one guide book put it, the ‘second string’ temples here would be star attractions at any other location. But the mind gets fatigued with too much visiting. So the best thing really is to just go to a few places and spend time at them and soak in the atmosphere. And don’t try to do too much on any one day. My schedule actually worked out very well - reached on day 1 afternoon, early enough for a quick trip to one of the temples ; went to 2 locations on day 2, one in the morning and one in the afternoon, and visit Siem Reap in the evening ; revisit Angkor Wat on day 3 morning and flight out in the afternoon.
From the guidebooks, I picked Angkor Wat, Bayon at Angkor Thom and Ta Prohm and those were the temples I went to. On the way from Angkor Thom to Ta Prohm, I passed Ta Ko another splendid structure and stopped there for a bit. I think Angkor Wat and Ta Prohm are must sees, you could pick the others to see based on reading about them and your personal interests since there is enough unique attractiveness to most of the temples.
A second visit to the place you most like is a good idea - it deepens the experience and there is almost certainly something you missed the first time round.
Since the temples tend to be large and have several kinds of things to look at, a detailed guidebook is a good thing to have It anchors you so that you are not wandering a bit aimlessly and you also can have an idea of what’s there to look out for. I bought one of these guidebooks so you could try getting it from me. A human guide is also a good option, the official guys there seemed pretty good.
The transportation arrangements to the temple from Siem Reap are not the best. I couldn’t figure out a better way so just hired tuktuks via the hotel which waited for me at the temples, which seemed inefficient. And worse, on one of the days, one the way back mixed up my tuktuk drivers and took the wrong driver and wasted some money. Its not just me being me :-) , the guidebooks also warn about confusion with tuktuks. The tuktuks also like to stick to two standard routes (Grand circuit, Little circuit) and you have to talk to them to get them to understand that you want to do your own thing.