Don't do the group tours of the wall. They are awful. They also take you to several gift hops along the way to try and make you buy stuff.
Simply take the train to the stop nearest the section of the wall you want to visit. I recommend Mutianyu. Exit the train station, and there will be at least twenty private vehicles waiting to take tourists to the wall. Most of them won't speak much English, but they know what you want, so there isn't much to negotiate. Both times I've done it the driver just slept in the car in the parking lot while we explored the wall. When we were done, we just went back to the parking lot, knocked on the window, and he took us back to the train station. Super easy.
Also, just one more note. There are lots of souvenir stands near the base of the wall. Be sure to haggle, and only pay about 20% of their initial asking price. Those stands ask astronomical prices hoping to prey on unsuspecting, naive, or confused tourists. Seriously, they will start by asking about $70-80 usd for a t-shirt. You can typically get them down to less than $10. Of course, they don't take USD's, so you have to do the conversions in your head while talking to them.
Also, if it's your first trip, allocate a day for Tienamen Square, and the Forbidden City. They are both very cool. Also, I recommend a half day wandering through some of the Hutongs. I don't remember which ones I've done, but they have all been very fun. We didn't do guided tours for the Hutongs (just wandered around ourselves), but I recommend one for the forbidden city. It's huge.
