Get a detailed inspection of the home before you make a purchase. A licensed and experienced home inspector may discover, for example, that the old wiring of the home does not meet current code. The foundation and structure of the home should also be thoroughly checked, to make sure there are no unexpected and extremely expensive surprises in store for you as homeowner.
Research the history of the individual house--your local historic commission will be a valuable resource here. A historical commission may even be able to provide you with historical photographs of the house from when it was built, which will give you clues as to historically accurate finishings and details which may since have been lost from the house. Find out whether your home is in a registered historic district, or is included in the National Register of Historic Properties. If it is, then there are limitations placed on what you can change about the house, particuarly on the exterior.
Have any issues with the home's electrical or plumbing systems attended to by experienced and licensed professionals. Bear in mind that a historically accurate renovation of a historical home will not include such luxuries as a modern shower cubicle.
Do any work needed on the floors of the home. The floors of a historical home are often in poor shape, and typically need sanding, staining and finishing. You can have professionals do the whole flooring job, or save money by doing the sanding, staining and finishing yourself. Alternatively, about half the cost of a professional flooring project can be saved if you hire professionals to do the sanding only, and complete the staining and finishing yourself.
Install missing woodwork and details of the home, such as crown moldings, rails, window frames and decorative woodwork. Use modern varnishes--polyurethane varnish with a satin sheet works well in historical homes. In homes over 150 years old, Shellac would have been the varnish originally used, but this is an unsafe choice due to its flammability.