This is a real big subject let me start with just a few things I've learnt over the last 6 years of owning a grade II cottage.
Firstly watch out for surveyors, your average surveyor will wander in with a damp meter and produce a report saying you need to install a damp proof course tell your mortgae lender and they'll insist on a load of unneccessary and possibly damaging work. They can also tell the difference between 200 year old wood worm and active woodworm!Get a surveyor with experience of historic buildings! SPAB should be able to help.
I don't know what sort of condition it's in but historic houses always need work - you're about to buy a hobby
As barb says you need permission to do work and it's a real good idea to get in touch with your local historic buildings officer early and have a chat so they feel comfortable that you want to work with them .
If it does need work - think about it - the house has been there probably for a couple of hundred years you don't want to make quick decisions that'll be hard to correct.
Spab also do courses on old buildings that are very good and have fact sheets and all sorts.
I guess the main point is to spend time enjoying living in a very individual home and take time getting to know it.
also check out
http://www.periodproperty.co.uk/