This isn't going to rock your world or anything, but it can make one of the little things in life a little bit easier.
Chances are your house/apartment/loft key has three little holes at the top, two triangles and one diamond. If you're like most people you just put your keyring through the diamond hole in the middle and never think about it again. If you're like me you try out one of the triangles.
As you can see, putting the keyring through the triangle on the side of the key with the teeth makes it much easier to identify your housekey by feel, and when you are putting it in the lock you know which way is the right way up just by feel. Of course if you put the key in the lock with the facing up then put your keyring through the other triangle.
Anyway, I hope you take the time to switch your key and make your daily routine that much easier!