I've driven most times, it's very straight forward. Via A406 follow signs to stadium (should take approx 5-20mins dependant on what time/traffic off the A406, biggest queue is usually the filter road off the A406, once off it flows well). Basically as you head into the trading estate that surrounds the stadium you will see loads of places/businesses offering parking. These are all non-offical parking which is fine, I'd argue it's better than official which is next the the stadium which takes longer to get out (never use the multi-story close to Wembley arena you will never get out of it, we are talking queues approx 2hrs!!). If you want to shave a few minutes off when leaving then take the carparks on the right hand side as you approach the stadium, as when leaving cars can only make a left turn onto the road (car parks on left hand side of road will have to turn right and there can be a few minutes slower). Expect to pay £20.