Caulk and seal up your home. Weatherproof anything you can touch.

Caulk and seal up your home. Weatherproof anything you can touch. Adding weather trimming to your main doors can be work for a few hours but it can really pay off. $1 for a tube of caulk and an hour of your time may feel like a waste since you may get only pennies back this month, but consider you weren't working at a job at the time, in a few months it pays for the materials, your home will feel more comfortable, and your HVAC  (heating and cooling systems) will not damage themselves so much when trying to keep up with your home. Adding insulation to your attic may be a messy and itchy idea that could be better left to a professional, though. You can even call inspectors that can use special temperature sensitive devices to monitor each part of your home to locate issues to improve.