There are a number of choices for parking in Lacock. If you look at the National Trust's website you may notice that they say that visitor parking in the village is not permitted. That is mostly but not entirely true. The small stretch of High Street between the junction with East Street and the abbey entrance can be used for free roadside parking if there is space there when you arrive.

The National Trust provide a fairly large car park which is pay & display, but free to members, and appears to be well signposted.

There is also a small car park with an entrance next to the Red Lion Inn which is free which the National Trust don't even mention. You would probably need to get here early to find a space.