Bath is a city in England.
North/West/East towards London, Cardiff, Bristol
Head to London Road and walk all the way down it until the roundabout. There isn't really any place for cars to pull in (no layby) but walk down a little and cars will be able to see you and pull in if they desire.
Coming from London / the west, there is a junction that heads to Bath with a layby just past the roundabout. Head there. You should get a ride pretty snappy.
Places to avoid
Accommodation and Sleep
Bath has spectacular countryside and it should be quite easy to camp out once walking out of the city in any direction (half an hour from the centre, more or less).