Been to Cambodia last year. It's a great place to visit if you want to learn the history of the nation there, how the Khmer fell by Communists cruelty. I recommend you visit the Killing Field in PP.
Siem Reap is a beautiful place, away from the hassle of the big city. It's peaceful and I travel by bicycle only to discover the whole town. I guess you have planned all the place of interest over there to be visited so I won't talk into detail about that. If you want to take the tuk tuk, let the hotel you're staying arrange it for you. The price should be cheaper if you do it like that. There's a Malaysian owned curry house in Siem Reap (I forgot the name), visit it if you have the time to.
Safety in Cambodia is one thing that you should be concerned about. Beware, really beware of pickpockets. Like any other traveller would do, keep your cash in few places, don't bulk it all into your wallet. People there will look into any opportunity to dig out your cash from your pocket, be it by buying their souvenirs to even selling you marijuana by the side of the road. Just be extra careful.
And if you plan to cheong, I suggest just keep that little brother inside the pants and forget about it. Unless you have someone over there that really knows a good place to Cheong and you cannot tahan sangat dah, then only take the risk. Personal experience, Cheong price 20$(wah wah good price), I walked back home realizing 100 Ringgit (I have MYR still at that time just in case) was stolen, while my friend lost 200$ off his wallet. The trick is they put a cloth hanger just beside the door, the girl will hang your clothes for you over there, and when you syiok banging the girl (which they won't change position so that you won't be facing your clothes), someone from outside the room will sneak in and take your money. It sucks bad(both the sex & the loss) and I stopped cheonging ever since.
There's a Muslim village you might be interested to check out in Siem Reap. Muslims there can talk Malay very well (they say their religious teachers usually comes from Malaysia) and they're very helpful to show you around the places. Since Khmer people don't speak English much, and ppl at this village are the ones that I could talk to easily, I was very grateful for their assistance during my stay over there.
protip when go cheong and clubs, bring only the amount needed to cheong. +/- a little more just.
never bring wallet, just cash in pocket.
one of my friend actually woke up in some hotel not knowing what happened the night before, with no cash and phone, haha.
so always go in group if possible and bring cash just. either that or put the valuables in your pants and roll it up and put under the pillow you sleep, haha.