A few pointers from a carpenter:
1.Check your door strike plates at your exterior doors, if the door seal is loose, you can remove the plate with a phillips and bend the "tongue" with a pair of pliers. Just a little at a time until the seal is tight. (Note: may also require deadbolt adjustment)
2. Check the floor seals on exterior doors. If it is drafty, many have an adjustable threshold, look for large phillips slots (usually 4). If the door seal is not adjustable, tou can pop the doorpins, or remove hinges from the doorside, get a slide-on sweep for the door at a hardware store for about $5-$10. At the very least, keep a towel against the door.
3. If you have a drafty window, a roll of adhesive 3/8" foam tape can fix gaps quickly.
4. Close heater vents in unused rooms, and cover with a strip of carpet or mat to seal the vent.
5. Unused basement space can be a heat sump in winter. A few fitted sheets of closed-cell concrete insulation board on the other side of the door can lock the cold down. Make sure it is airtight, stuff gaps with roll insulation or use expanding foam.
I'll post others as I think of them. This can save you a fair bit of money in your power bill.