Wool has a tendency to shrink so be careful washing things. Linen will shrink slightly – I always wash my new linen on a hot wash, then it has already shrunk and I don't have to worry about my shirts and shifts shrinking. Obviously underclothes should be washed regularly, but think of doublets, dresses etc. more on the lines of coats. A certain amount of dirt is fine and is, in fact, encouraged as we are trying to portray real people in real clothes. The best way to wash larger items like dresses, is in the bath! Try not to use biological powders, especially when washing white items, as the optical whiteners in them have a tendency to make things glow.
Remember to wash and iron all fabric before you cut and sew it. I did not do this once, as I was desperate to complete my new dress – the result was that the wool outer and the linen lining shrank at a different rate and resulted in an utter mess. Due to cooking hazards, I only wore it once before it was washed! So be warned!