You could always pre focus in manual mode on a given distance, usually with a wide angle and stopped down a bit you can get a huge zone of "acceptable focus"
Then just shoot from the hip, just take the shot as if people were kind of in the way of what you were really shooting, great for candids.
If you really want close "one on one" always ask permission, you'll be surprised by the level of cooperation you will receive from most folk.
Also remember that depending on your final use of the image, you may require a model release to be signed.