Offer foreign traders unrestricted trading rights in this country. You will have to dramatically increase taxes on local traders, but right now it is more important to encourage foreign trade to Scottish ports.
Grant certain burghs the right to trade. Only these burghs can hold markets and sell goods.
Good advertising does encourage trade. However, with no internet, newspapers or television news travels very slowly. You have to work a little harder to encourage foreign traders to your ports.
Which card are you going to play?