We really enjoyed our time in Laos. Here are some things that might help you mentally prepare for your trip :
Even though some things don't seem as developed as Thailand, it's actually nice in a way. Things are sold mostly in little family-run shops and not in big chain stores so you won't find 7-11 everywhere. Even in fairly Westernized places like Luang Prabang, you can still see vendors carrying bamboo baskets and women wearing traditional long skirts.
More nature means there are lots of bugs everywhere and yes, it's southeast Asia so don't be surprised you get diarrhea once in a while - It's fairly common for dishes to be washed in a big pot just on the side of the road.
In all the hotels and guesthouses we stayed at, there were not so many power outlets. If you have a few electronics to plug in, perhaps bringing a small power bar would be helpful. There were quite a few power outages during our 10-day stay in Luang Prabang although most were resolved within a couple of hours.
You can find wifi quite easily in Luang Prabang, Vang Vieng, and Vientiane, but Internet is almost always quite slow. Uploading or downloading something requires a lot of patience. Internet connection is significantly faster early in the day, before 9 am. Like wise, hot showers are pretty standard, but water pressure tends to be on the low side if you actually want "hot" water.
If you think that less development means that the air is always fresh, note that quite often somebody is burning something. You'll also likely notice garbage along roads, riverbanks, and in rivers. At first I suspected it was the tourists who're ruining this beautiful country, but then I saw quite a few locals littering like like nobody's business. Occasionally, you might see people spitting on the ground or discarding things out of the window/balcony.
It's also not quiet all the time, partly due to the lack of soundproofing. Some households might be playing music so loudly that the whole block could hear, even really early in the morning. Nature noises like roosters at 5 am or dogs barking are also to be expected. Bring earplugs if you're a light sleeper.
True, there are many friendly locals, but don't look forward to smiles all around. A lot of people might seem curt or even pissed off, at least initially. Even in hotels or on tours, things tend not to be explained. For example, if you're taking a long distance bus and the driver stops for lunch, chances are he won't tell you where to get it or how long you have - you just have to see what everyone else is doing. Maybe it's due to language gaps, often your questions won't really be answered so keep that in mind and don't expect too much.