Pretty easy, book tickets in your guesthouse or in one of the travelagencies in Siem Reap.
Bus leaves in the morning, rides up to the border, leave Cambodia, enter Thailand, small mini bus takes you to a new big bus, drive to Bangkok.
Took us in grand total +- 10h if I am not mistaken. Just make sure you stick to the group at the bordercrossing (you will gat a coloured sticker, you ll see)
#2 Lawoat has been a member since 29/6/2009. Posts: 59
The bus we got didn't go from a bus station - just from a petrol station to the west of town. So a tuk tuk picked us up at our hotel and dropped us there - so I wouldn't worry too much about where you stay, somewhere in the centre will be no problem.