Consult an architect before starting any major renovation of a wood-framed house to be sure no structural elements are involved. Altering the wrong wall could affect the stability of the house. Have an electrician and a plumber check any kitchen or bathroom updates or any major additions. Adding circuits may require another breaker or even more service from the power company. Adding a bathroom could involve more basic drainage or sewer connections. Review design and remodeling books for ideas and suggestions.
Plan any remodeling carefully. Sketch a floor plan of the area on graph paper and draw in all changes, in walls, doors, windows, sinks or other elements. Measure existing spaces carefully and calculate changes by getting sizes of cabinets, windows or other components. Make sure everything will fit; nothing will spoil a remodel quicker than having a cabinet arrive that is 6 inches too long for the allotted space.
Decide how much you can do and how much will need to be contracted. Tear out old wallboard or plaster, remove baseboards and trim, but leave building new wood-framed walls, installing windows or doors or hanging and taping drywall to professionals. Hire all electrical and plumbing work unless you are licensed in those areas; most jurisdictions require licensed electricians or plumbers on any remodel.
Talk with contractors and get estimates. Ask what help you could give -- painting a wall, caulking around windows and doors or adding trim. Compare prices and check references and recommendations. Don't hire a contractor who is vague about costs or work schedules. Get all estimates and commitments in writing.
Consider finishing a basement as an easy way to get more space with less structural change. Relocate heating/cooling ducts and build walls to conceal posts and columns. Waterproof walls completely and paint them. Add lighting, with an electrician. Install tile flooring or weatherproof carpet.