Explore with a boat (stay near coasts still) and gain visibility of more clans, then setup trade agreements with the ones you won't be warring with for a while. Be a cheapskate with agent actions (some of them are free or little cost, whereas others cost a bomb), and I was always keen to increase the development of roads and markets (so long as I had surplus food, I was always a farm whore too first and foremost as it also allows for fortifications up to the point of having 'free' troops in the garrisons).
Get hold of something like a gold mine, and you may want to park a metsuke in that province's fort ("oversee city") to boost it's trade output too.
When it comes to taxes, I started out about the 2nd or even 3rd level up if I dared, but now I just try to play the game through keeping tax on the lowest setting the whole time. With the surplus food and decent city development, the growth of the towns increasing each turn stacks up. At one point I was getting like 9k per turn and I'd have to spend around 13k to negotiate a peace treaty w/trade agreement attached (I was lucrative on trades so that helped keep the price 'down' !).
Last thing I recall, is that some of the missions and rewards allow you to make a choice between lump sum, or increased growth, for a number of turns (around 8 typically), and once you start to get a few provinces under your belt the +growth one is a healthy boost to the coffers.