Many times, drafts around windows or doors are simply due to gaps in the caulking. Check around the perimeter of the window or door where it meets the frame or the wall to see if you spot any gaps. Over time, caulk will dry out, shrink, or peel away from the seams. Also check around the casing (trim) for gaps in the caulking. If you see gaps, remove old caulk and re-seal with new caulk. If not, you may need new windows.
Cold Floors or Walls
If your floors are cold to walk on or your walls are cold to the touch, you probably have little or no insulation below the floor or behind the wall. If you can access the area under the floor (via crawl space or basement), check for insulation. Install insulation where missing or replace damaged insulation. If your flooring is directly on a concrete slab, you may want to consider installing radiant floor heating. The only way to add insulation to your walls is to remove the drywall (or plaster) from the interior of the wall, inspect, add insulation, and install new drywall. If you want to minimize drywall removal, you may be able to remove small sections in certain areas and have insulation blown into the walls.
Some Rooms Warmer/Colder Than Others
First, check your register vents and/or radiators to see if they are open and working properly. Another cause could be more/less sunlight in that area of the home. If you get more direct sunlight in a certain room, window coverings and treatments can make a significant difference. If you have older windows, you may want to consider upgrading to new, energy efficient windows.
Spots on Roof With No Snow
If it's winter and you've had a significant snow, take a look at your roof. If you notice a few areas where the snow has melted or never accumulated compared to the rest of your roof, you may have some missing insulation. If your attic has some areas with insulation missing under the roof, the heat will be able to escape through the roof, creating a warm spot and melting any snow that falls in that area. If you notice that on your roof, it's a good indicator that you should check the insulation in your attic. You may be losing quite a bit of energy in those spots! The simple solution is to add insulation in any deficient areas.
Utility Bills Higher Than Usual
If you notice that your recent utility bills are higher than usual, you may have some energy efficiency issues to address in your home. Some are very simple, others require more work. If it's a heat wave in the summer or a real cold spell in the winter, it could just be a normal increase in your gas, oil, or electric bill based on the extreme weather. However, you should check the efficiency of all your HVAC systems. The first, easiest check is your filters. If your filters are haven't been changed in a while and are clogged, your HVAC system won't run as efficiently, which will be especially noticed in extreme conditions. Most filters should be changed every 90 days. You may have drafty areas around doors or windows. They could just need some caulk or weatherstripping to seal them better. If they are older, you may need to examine the framing and door/window to see if any repair or replacement is needed. One other common cause is insufficient insulation in certain areas. Check any accessible spaces (attic, basement, crawlspace) for missing insulation. You can also feel your walls to locate hot or cold spots that may need new or added insulation.