If the camera support AF assist illumination, use it. It will light up the subject for better focus tracking.
Also, if not specified, the camera will decide on which AF points to use, which may not be what you want. Try to select a AF point for the operation and aim that AF point at the subject(model).
From the picture, it is quite apparent that the car offers better contrast compared to the model. If you can, ask the model to wear something of high contrast (e.g. black and white). It may help a little, althou the effectiveness varies.
Or, like what other mentioned in another thread, try tp light up the model with a torch or something, after focus lock then switch it off, then take the picture.
but no matter how i shoot i could only get the car in focus... but not the human...