You can dramatically improve the accuracy of your traces by putting your GPS where it can get a good signal. Remember that it needs to have a good signal all the time, so even if you seem to get a good signal while you're looking at your receiver, it could drop in strength when you put it away.
If you're walking, the best position is in the top pocket of a rucksack, or attached to the shoulder strap. Having your GPS in a pocket on your lower body will seriously reduce the accuracy of your traces, as your body will block at least half of the sky.
If you're cycling, a handlebar mount for your GPS will give it a good view of the sky, while still making it easy to add waypoints. A rucksack is another option.
In a vehicle, it's more difficult to place your GPS where it will be able to see most of the sky. External roof-mounted GPS antennas are available, but they're not cheap and involve drilling a hole in the roof of your car. The best location is as far forward...