Yes, what if you have decided to move to Cambodia? Well.. after almost 6 months of Cambodia here are my advice.. hope you enjoy! :)
Have a GOOD health insurance - I really mean it. If you want Western style medical treatment you better have a very good health insurance OR a lot of cash in your pocket. Myself I had the "opportunity" of being hospitalized due to kidney stones in a private hospital and the total bill was US$ 2,000 that thank God my insurance covered.
This is NOT play land - There's prostitution, there's a lot of corruption, there is some overall disrespect for standard society rules. That gives you the right to play like the song? NO. Do something good and DO NOT fund prostitution (I will not even mention about pedophilia). DO NOT buy books from the kids at US$1 in the Riverside area. DO NOT drive like crazy or disrespect the "universal" traffic laws. DO NOT look down at Cambodians. DO NOT fund begging behavior. DO NOT litter because everyone does. And everything else that you wouldn't do at your country, don't do it here.
However, IT'S NOT your country - So do not expect to have that big fancy mall waiting for you (there are malls but are not big and not that fancy). Also do not expect people to behave like you are used because naturally they won't and keep screaming in the middle of the street that someone didn't stop for you to cross it won't solve. GIVE the example instead.
DO NOT bargain for nothing - How much would you pay for a meal in your country? and a book? and a taxi? or a beer? So do not bargain that hard for nothing. If you're not from Southeast Asia (some countries) or Africa, it's very likely that EVERYTHING here is much much cheaper than you are used to pay. It's really not worthy to keep arguing with the local people for $0.50 or $1 that in the end won't make any difference for you but that WILL make a great difference for them.
Enjoy the GOOD things - that you will be able to notice that the tourists cannot. If you stay more than 3 months you soon gonna notice that a new plaza has been built, a new building has been refurbished and now looks very pretty, the nice old French plazas are extremely nice, the Riverside area is incredibly beautiful, etc..
DO NOT emphasize the bad things - since you are a long term person you gonna notice the lack of respect (or notion) of the rich (mostly) Cambodians driving their out of proportion big cars anywhere. The overall Cambodian people littering everywhere and buying things that they don't need with money that they don't have. Anyway, you gonna see exactly what the happy short term tourists won't notice and Lonely Planet won't tell you SO manage your feelings. It's really not good to feel anger about that and won't make it any better. Instead, try to convince people to change. Take ACTION!
Live LOCALLY - Which means.. try to spend like the locals do, try to eat what do they eat and go to their places. Soon you gonna notice that is incredibly cheap, good and you gonna get lots of fun and close to them.
BUY A BICYCLE! DO NOT BUY A CAR! - Yes! Buy a bicycle, around $30-50 second-hand, and ride it everywhere for free! Give a good example to the locals! Do not buy a car because the streets are small, there are car exclusive traffic jams everywhere and since Phnom Penh is totally plain and quite small there's absolutely no need to own a car here.
Buy CAMBODIAN products - I agree with you that there are not so many options but there are some. Pay attention to the country of manufacturing of the products and always when possible choose for Cambodian made ones. It's extremely important to help the local industry to develop and it's the interest of the neighbor countries that you keep boosting importation.
Get the HOLIDAY calendar - There are many holidays in Cambodia and you will be able to enjoy them and get the best perks if you plan ahead. Make good use of planning and you will be able to transform those holidays on good trips.
UNDERSTAND - Cambodia went through civil war from the 70s to the late 90s therefore people had not too many feelings different from thinking about their food or their survival. Which means, they are not used to modern free feelings. Cambodians may not deal very well with passion, love, frustration, money, anger, or any other common stuff like that. They may get terribly depressed about a love frustration and put it all publicly. They may spend an amazing amount of money with silly and unnecessary stuff even if they're poor. DO NOT blame them, help them. Bring your experience since you have been taught how to manage that kind of feelings since you were a kid.
BE a celebrity - People still are not used to foreigners and anywhere you go you gonna attract people's attention. You gonna really feel like a celebrity. Sometimes people will keep starring at you so just look at them and smile and you are likely to get a nice smile back.
IT's NOT personal - When you are driving your bicycle around town you will be likely to get some horns from all type of drivers or even have to suddenly action the breaks not to hit a driver OR you gonna both stop in the middle of the street. Usually despite all that mess people will just smile and even if you have almost hit each other he/she won't be angry and probably won't scream at you.
BE safe - which means DO NOT let to go home too late at night alone and with valuable stuff with you. Phnom Penh is still a "countryside" city and gets incredibly empty after 10 pm. If you get back drunk and talking out loud in English (or Chinese/Japanese/etc) you are most likely to be an easy target. So, be careful. Do not take fancy cameras, passport, credit cards with you at night. Better, do not take any thing that can be snatched from you. I'VE SEEN IT!
Again, PLAN to travel abroad - It's not easy to travel from Phnom Penh to anywhere except Ho Chi Minh, Bangkok and Kuala Lumpur. All the other big cities/countries you may have to book your ticket very early or have plenty of time to go since there are not many cheap direct flights and you will have to go to Kuala Lumpur or Bangkok to get a connection.
HAVE an amazing experience with this wonderful and lovely people! :)