If you are going to Dunkeswell you'll need to book the table in the Air Centre in advance as it is popular. Don't leave it too late as they do ease down after about 14.00hrs
The route I use is a simple one -
EGTR - Overhead Booker -Henley - Membury -Devizes - Glastonbury - Dunkeswell.
The southerly route Henley - Popham - Alderbury - Shaftesbury - Sutton Bingham Reservoir (south of Yeovil) - Dunks is a prettier route but more congested.
Both Old Sarum and Compton Abbas are good places to stop en route.