Beijing is a flat city. So if you have a good physical condition, choose a hotel in the city center and go around walking. Is the best way of know a city. Sometimes we used the subway, but I didn´t felt a need of use bus tours (except to go to Great Wall).
Walking in Beijing has its pluses and its minuses. I definitely recommend walking to and from some places, depending on where you are. The buses can be difficult if you don't speak Mandarin/Chinese. The subway is easy, convenient, and cheap, but it does not go every where, so you will have to do a little walking even if you do take the subway. Taxis can get expensive.
The pluses of walking is that it is free, a good form of exercise, and it gets you exactly to where you want to be. It will also give you an opportunity to see Beijing instead of being in the subway or in a crowded bus, not sitting next to a window.
The drawbacks of walking are the air is not that great in Beijing. You could get lost if you don't know how to read a map. The biggest draw back is that pedestrians do not have the right of way. Even if there is a green light for walkers, cars still drive. Cars don't stop for anyone, even wheelchairs. It is pretty crazy to see.
But there is method to the drivers madness and in the entire time I was in Beijing, I never saw an accident with a pedestrian. The best advice I can give is to be confident and just go when the green light tells you to.
Walking is a great way to get a feel of a new city, so feel free to take to the streets and wander. I felt extremely safe as a single female walking at night. Be aware that Beijing is a huge city and the city blocks are deceptivel large so bring some water and have a walk around!
Central Beijing is a flat city - no hills or mountains etc so I did a lot of walking around Beijing. It is a safe place to walk even at night. Just be careful not to walk in front of people on their bikes. But be warned things that look close on a map arent necessarily as close as you think. But it is good exercise & I was a lot fitter afterwards.
Everywhere we went in China, our tour guides were terribly concerned about our walking the city streets due to the crazy traffic. They all inevitably said the only way to cross streets was to find a local and cross with them.
It's been my experience that walking is the fastest form of transportation in Beijing, at least for short-intermediate distance anyway. The traffic hasn't moved since the Ming Dynasty and the 'subway' doesn't take you to a whole lot of places.