I only want to add that this is critical advice. My wife is Chinese and, of course, fluent in Mandarin (her first and primary language). Even so, so many taxi drivers come from the provinces that, frequently, they have trouble understanding her. Non-fluent Mandarin speakers shouldn't even attempt to manage without the destination written in characters (though I suspect, "airport" in English would suffice). We've also had to call our destinations numerous times so they could give the driver directions. There have even been instances where we simply had to abandon the cab and find another that was more familiar with Beijing.