Why take the bus?
While the train network in China is expansive, the bus network is even more so. Trains connect larger cities and of course have stops along the way. But there are hundreds of towns and villages where trains don't go and these are connected by bus. If you are really hoofing it and seeing the countryside of China, then you'll probably find yourself taking a bus or two.
Considering Bus or Train?
If you have the choice between the bus and the train then it pays to compare prices and also comfort.
On the train you can get up, move around and use the restroom. On the bus, you're pretty much stuck and also subject to traffic on roads that can become choked with traffic. However, the bus may get you where you need to go, where there aren't any train connections. And usually, bus routes are less expensive than train routes.
Figuring Out the Bus
To find out bus connections you can of course look them up online, but information online can be unreliable. Local travel agencies should have the most up-to-date information and might even be able to help you purchase tickets in advance. If this isn't an option, ask someone in your hotel to help you find out about bus schedules and if they can't (or won't, although I can't imagine hotel or inn staff not helping), the most reliable way to directly to the bus terminal itself. Tickets are usually purchased the day of travel, often on the bus itself.
Different Types of Buses
Buses can differ based on the route and proximity to large cities. Generally speaking, buses from large cities, on the Shanghai – Hangzhou route, for example, are new and clean. You might find buses on more remote routes less new and less clean.
Buses on smaller routes might be more like minibuses that don't depart unless they are full.
It's best to be patient on these small routes.
On longer routes, there are sleeper buses that travel overnight. Each passenger gets a sleeping berth in order to spend the night in relative comfort on the overnight journey.
Highways and Roads
Roads are being constantly improved and new superhighways are being built all over China. For example, work on the G6, a highway that will connect Beijing with Lhasa is in progress (it currently ends in Xining). But as quickly as roads are improved, people are buying cars and roads can get extremely crowded, especially in high-travel seasons such as October holidays and Chinese New Year. The most horrific was a sixty-mile traffic jam into Beijing in 2010 that lasted for weeks.
Hopefully you and your bus will not be caught up in anything quite so dramatic but don't be surprised if you do hit some amount of traffic along the roads.
On any public bus, especially a long-distance service, there will be scheduled rest stops. As you exit the bus, the driver will probably signal to you how many minutes you have. If not, try to find out so you know how long you have.
Don't expect too much from these roadside service stalls. There will be a small shop selling basic supplies like dried snacks and drinks.
There will be bathrooms that will hopefully be relatively clean, if not comfortable. Roadside stops usually have only squat-style toilet facilities.
Do take the opportunity to use the facilities and stretch your legs. But make sure you remember where your bus is parked so you don't miss the rest of the journey!
Preparing for a Bus Journey
If your journey is short, then you probably don't need much besides something to read and a bottle of water. However, if you're on a longer journey, you should bring some snacks along. You'll find the locals have an endless supply of snacks and drinks to while the journey away. I've found mandarin oranges and sunflower seeds seem to be some of the most popular local snacks. Bring along a plastic bag to keep your garbage in as well.
While I've lived and traveled in China quite a bit, I have not taken many public buses.
The trip to Hangzhou was fine but on our return, a Sunday evening, we got caught in traffic and what should have been a two-hour journey was a six-hour trip. One can never be certain to avoid traffic jams but if you avoid rush hour and peak times, you may have better luck.