At Tain, join the long-distance walk from Inverness to John O Groats and follow the instructions on it's website for stages 4 to 7. This walk is a 'work in progress' following the coastline. If for some reason you do not want to take this path, you could simply follow the A9 but this is a less attractive option as the road can be very busy and there is not an official footpath, leaving the walker to cope with sometimes narrow verges.