One of the most cost-effective ways to make your home more comfortable year-round is to add insulation to your attic, including the attic trap or access door, which is relatively easy. To find out if you have enough attic insulation, measure the thickness of the insulation.
If it is less than R-30 (11 inches of fiber glass or rock wool or 8 inches of cellulose), you could probably benefit by adding more.
If your attic has enough insulation and proper air sealing, and your home still feels drafty and cold in the winter or too warm in the summer, chances are you need to add insulation to the exterior walls. This is more expensive and usually requires a contractor, but it may be worth the cost-especially if you live in a very cold climate. If you replace the exterior siding on your home, consider adding insulation at the same time.
You may also need to add insulation to your crawl space or basement. Check with a professional contractor for recommendations.