To get to Canterbury by car, take the A2 or M2 from London and follow signs to Canterbury. From Brighton, take the A27 and then join the A2. There are also various bus services to Canterbury from surrounding areas.
If travelling by train, Canterbury West and Canterbury East train stations are both located in the city centre and are easily accessible from London, Ashford, Folkestone and other local towns.
If you're travelling from Dover, take the A2 or M2 towards London and exit at Canterbury. From Maidstone, take the M20 and exit at junction 7 for the A249, then follow signs to Canterbury. From Tunbridge Wells, take the A21 and then the M25 towards Heathrow, before joining the M20 and exiting at junction 7 for the A249.
Overall, driving is likely to be the quickest option for most people, especially if you're travelling from further afield, but trains offer a comfortable and stress-free alternative.