This is the most common way to prove the first element of DUI. The person is seen driving by the officer. There is not much dispute about this element when the officer sees a person driving.
Actual Physical Control
This is a little tricky. Actual Physical Control allows the jury to consider all circumstances as to whether the person was in actual physical control including: how did the car get there, was the person awake or asleep, was he seated in the driver's seat, where were the keys, how long was the car sitting there. From my experience, juries do not like to convict on these types of cases.