Safest method I know:
Point the gun in the safest possible direction (a phone book will stop a .22LR from a 7" barrel in my experience) just in case.
Pinch the hammer so that the firing pin is between the outermost knuckles of your off hand thumb and forefinger. The goal is to position your hand so that it is NOT in front of the muzzle but if you do drop the hammer you'll just pinch your skin.
Pull the trigger and lower the hammer slightly.
Release the trigger.
Lower the hammer down steadily until it comes to rest on the half-cock notch.
At that point you can turn the cylinder with your thumb and forefinger so that the hammer slot is lined up. Then, still holding the cylinder, place your thumb on the hammer spur and pull the hammer back slightly (just a little bit, not enough to cock), pull the trigger, and with the trigger held lower the hammer with your thumb while guiding the cyclinder as needed so that everything clicks.
I don't have one in front of me so I'm going by memory but I think that's the "safe way".
You can also just hold the gun normaly, grab the cylinder with off hand thumb and forefinger, put your strong hand thumb on the hammer spur and pull back slightly, pull the trigger, lower the hammer a little past the half-cock notch, release the trigger, turn the cylinder w/ thumb and forefinger, and ease it down the rest of the way. It can be quite a fluid motion if done right. Not quite as safe though.