The Great Wall at Badaling can get very crowded, especially during the peak tourist seasons of May, September and October. The first week of October (called the "Golden Week") is the national holidays of China and a lot of tourists will be there, so please avoid if possible. Be careful of your belongings and it is best to keep your valuables in front of you or in your waist pouch (best is not to bring them if possible).
Some portions of the great wall at Badaling are rather steep (and others with huge and uneven steps) so be careful especially coming down. There are railings at the side along the wall (see photo), so hold on to them if you need to. At the other parts of the great wall, especially the Simatai Great Wall, some parts of the wall are in bad condition so be extra careful if you are there. Take a rest if you are tired, as it is not easy to go all the way up without stopping.
Be careful, as it can be very hot while climbing the steps towards the Great Wall.
So wear a sun hat on your head, use a sun block crème, and of course take plenty of water.
But if you do not have enough water, there are small stands on the Great wall, which sell drinks, but these drinks can be more expensive then from an ordinary shop. But whatever, when you are thirsty.
The picture proves how hot it was; even the camel was wearing a sun hat.
I did not see this while I was visiting Egypt, so maybe it was even hotter then in Egypt.