It can be a shocker geting out of there in a car.
If the tube strike does go ahead, then it will be 10 times worse
I have parked at stanmore and its just a couple of stops on the tube, but need to be early as its busy
I always get the train from grantham (subject to tube strikes of course) you can get a return to kings cross for £30 per person for off peak travel, you can pay nearly that in parking.
If you fancy a swift pre match beer the I highly recommend the Green Man on Dagmar road
http://www.multimap.com/maps/?qs=wembley+stadium&countryCode=GB#map=51.55628,-0.28296|17|4&bd=useful_information&loc=GB:51.55581:-0.27955:17|wembley%20stadium|Wembley%20Stadium
They have a car park which you can use! its not rammed like a lot of the pubs near tube stations but has a great atmosphere
Dave Parnell