Be prepared to share your space with lots of people.
The Forbidden City is huge, but we hardly imagine how could have lived there about 8000 people.
I think that the simultaneous visitors will be less than that, but we are always surrounded by a crowd, and all the places where we may peep must be seen behind a wall of heads or... cameras.
Fortunately, the most interesting things are outdoors.
Everywhere and every time.
The great wall follows the rules, and it is a long stripe of people slowly gliding upon a rocky construction. No matter where you look, there is people.
Try to make a picture, and, even being selective, it will be filled with strangers. So, give up! People is life! And China is... millions of people.
You're in the capital of the third largest country in the World, whose populace make up one-sixth of the human numbers on Earth. Really, don't expect to have your private space when you are visiting tourist sights, especially at the Forbidden City and the Badaling section of the Great Wall!
People push. People shove. People cut queues. People turn nasty. People shout. People spit. People give each other dirty looks.
Hey, welcome to Beijing!
Travelling to Beijing on wheel chairs is a real problem. Almost all the monuments such as Forbidden city, summer palace and great wall are full of steps and staircases. Unless there are people to help move the wheel chair, some of these places are inaccessible if on wheelchairs.
As you see it´s very crowded. Normaly I wouldn´t visit such a place in the main holiday if I have been here before. But when I was there the first time the weather was terrible and I couldn´t take any good photos... so I had to visit that wonderful place again. And I didn't regret it. Anyway, if you have the chance to visit such a place, don't choose the first week in May or October. (or during Chinese New Year in February)
When I was in Tian'enmen Square the was a small demonstration in favour of the Falun Gong. The protestors were very quickly rounded up by police and taken away in minibuses. Also the police confiscated the films of anyone who they suspected of taking any photographs or videos of the happenings. And as a large number of the police were in plain clothes, mixing with the tourists and visitors they were able to keep an eye on everybody around.
In Beijing as in most crowded Chinese cities, you really need to watch your step and stay on your toes. Anywhere there is a crowd, hold onto your bag - carry it in front of you, not behind your back, and keep your eyes open to what's around you. People will walk into you. You always have to keep looking around so that you don't a) walk into people, b) get walked into by others, c) get run down by a bike. That's one thing that's not so fun about Beijing and China; in many places, you can't just stand still and look around and relax without getting mowed down. ^_^.
This advice is doubly true when you're crossing roads. Go when everyone else does and be very cautious - good reflexes are useful, being ready to stop walking abruptly or start walking quickly. Cars and bikes do not give way to pedestrians; pedestrians have to look out for themselves even at many of what are ostensibly pedestrian crossings.
It's good to just try to keep a good humour and not let yourself get irritated by the crowds. After a few days you'll probably become a bit more vigilent, and also more pushy. Because many places are crowded, people are more forward in doing things like pushing into queues, not apologising when they walk into each other, that sort of thing. In queues or places where people are all trying to see something, just stand your ground and don't let others push you out the way, or you'll never get your turn!
If you want to travel to Beijing, do remember to avoide the tourist peak season. It is so crowded that you will find there are all the people in every scenic spots. Oops, it is a terrible experience if you try to make your way out of crowd.
It should come as no surprise that the Forbidden City and the Badaling Entrance to the Great Wall are very commercial (this KFC is within a stone's throw of the wall)with very large crowds. You will be hit hard by hawkers at both. These are not quiet spots to contemplate Eastern philosophy. Expect that going in and you'll be better off. I would suggest on the Great Wall, however, that the farther you climb the more you are able to escape the crowds and hawkers.