Don't book any trip between Thailand and Cambodia by travel agents. Travel by your own, it's cheaper, faster, less hassle.
BorderBe prepared to pay much more for a Cambodian visa at the border than it effectively costs.
MoneyDon't change more than 10 USD into Riel. Everything is being payed in USD, change is in Riel.
TemplesGet a three day pass for 40 USD. It's the same amount as for 2 days. To avoid temple sickness, have a half day break at the second day and go to the floating villages.
Angkor Wat, Angkor Thom (Bayon) and Ta Prohm are musts, don't forget Banteay Srei.
Avoid Chaweng beach or rather go to Benidorm, Rimini or Playa del Ingles if you like that kind of beach, you spend less time and money for travelling (....talking to Europeans).
Avoid beachfront bungalows at Hat Rin east beach. Beach parties can last all night long and techno sound hardly helps you to fall asleep. And by the way these parties do not only take place at full moon.
Start your holidays in Banglampoo (Khaosan area) to get into the traveller community, spend your last days in Sukhumvit because you got fed up with them.
Have a drink at the Skytop bar of Baiyoke II tower for 200 THB, if possible during and after sunset.
Airport tax is not required anymore.