There is no usable car park at the ground and nearby street parking is limited. The Parklands Social Club does allow some parking at £4 per car (See Where To Drink). Otherwise there is a free 'Park & Ride' service to the ground operating from Cheltenham Racecourse, which is well signposted around the town. Journey time on the 'Park & Ride' service is obviously dependant on traffic, but is around ten minutes on average.
That said, I'm planning to get to Cheltenham fairly early and look for some street parking. There must be something somewhere within a mile of the ground!