Go temple-hopping around Angkor Wat
There’s no right or wrong way to explore Angkor Archaeological Park, but you can be strategic about it. Start with official 'Wonder of the World' and the largest religious site on Earth, Angkor Wat but get up early to see it at sunrise as they'll be a lot of people with the same idea. Alternatively, go for a hilltop complex like Phnom Bakheng at dawn to avoid crowds (most people visit here at sunset).
It's best to do most of your exploring before the midday sun hits, although the 'Tombraider Temple', Ta Prohm, is a good one to go to in the afternoon, as it's shaded (read: half-eaten) by tightly-knotted banyan trees. Get the three-day temple pass ($62) if you're here for anything longer than a weekend break, as it's worth taking time to explore the smaller, off-road temples like Preah Pithu, in and around the main city of Angkor Thom.