Fly choice will depend on the time of year. In the spring and autumn weighted tube flies may be required, but if the water is low flies tied on larger doubles or trebles will be sufficient. In summer bring doubles and trebles down to a size 10 or even smaller on some tributaries. The most popular patterns nowadays tend to be variations on the shrimp fly theme. A good tactic is to work the fly when it is in the water, getting the dressing pulsing can produce many a fish when there seems little opportunity.
It is advisable to contact your ghillie for up-to-date information on what is best for your trip.