The main thing worth planning around is when you leave London. Setting off before the weekday morning peak, or after it has cleared, keeps the drive out to Warwick Castle shorter, and your driver will suggest a departure time that avoids the worst of it. Weekends and school holidays are busier at the destination itself than on the roads, so an earlier start usually buys you a quieter first hour on site.
It also helps to tell us your group size and any luggage or pushchairs at booking rather than on the day. Four people travel comfortably in a saloon; an estate, MPV or 8-seater covers larger groups, shopping or child seats, which we fit free on request. Warwick Castle gets busiest in summer and over school holidays, so booking with some notice makes it easier to secure both your date and the right vehicle.
If your Warwick Castle day starts or ends at an airport rather than a hotel, mention it when you book so the whole thing is planned as one itinerary, with the flight tracked and luggage accounted for, instead of several separate journeys.