Lets start with a cycle route planner. The links below show route finders which can help you plan your cycle ride.
The first is a route finder from Cycle Street. It can help you find the best route to the shops, work or a friend's house in your local area. Enter post code of start and finish or use street names or build names and up pops your route. There is a main map with fast, balanced and quiet routes, plus mini-maps with Google Street View on each listed section. Good and worth a play.http://www.cyclestreets.net/
The National Cycle Network running through Wiltshire and West Berkshire
National Route 4 is a long distance route between London and Fishguard via Reading, Newbury, Devizes, Bath, Bristol, Newport, Swansea, Carmarthen, Tenby, Haverfordwest and St. Davids. The route is fully open and signed throughout the routebut has not been finalised in central London between Greenwich and Putney Bridge.
National Route 4 splits in Wiltshire one passes through Trowbridge, Melksham, Chippenham, Calne, Avebury, Marlborough, Newbury and the other through Devizes, and numerous small villages to Newbury.
The Kennet and Avon section runs from Reading to Bristol and has a lot of traffic free cycle ways.