I think your question probably should be, how do I get more accurate auto-focus, not faster.
Make sure you're seeing a focus issue and not a motion blur issue. What was your shutter speed?
Make sure you're focusing where you think you're focusing. Don't use multi-point AF for a portrait, as the camera will focus on the highest contrast, or in some cases the closest object.
The focus priority Derrel mentioned is the default setting, but both can be changed in the menu. AF-S defaults to focus priority, meaning the shutter won't release if the camera hasn't focused. AF-C defaults to release priority, which means the camera may make an effort to focus but doesn't wait for perfection; it takes the picture. Both focus modes can be set for either focus or release priority.