Fred Asbell taught us this in a class many years ago, and since then I've nocked just about every arrow I've shot the way he taught us.
You hold the arrow with your thumb on one side of the nock and your forefinger on the other. You swing the shaft over against the riser and then lower it onto the shelf. You lightly hold it in place with the forefinger of your bow hand as you slide the arrow forward. You move the nock end of the arrow over against the string, higher than the string nock, and as you're sliding the arrow forward you're also sliding it down the string. When the arrow nock reaches the string, you slide it down the string until you feel the bump as it slides over the string nock. At this point, you slide the arrow forward and let your thumb and the arrow nock go on one side of the string and your forefinger on the other, so that you end up still holding the arrow nock with your thumb and forefinger in front of the string. Then you pull the arrow nock back onto the string and up against the string nock.
Fred didn't care which way the cock feather ended up, as he said it didn't make enough difference to matter at the hunting ranges he uses. You could use indicators on your arrow nocks, if you wanted to, or just glance down before you seat the nock and give it a twist unless it really has to be a blind shot.
I just really like this way of nocking an arrow. I always tell my students that people will already think they're a good shot if they nock an arrow this way. They don't actually have to shoot the bow; they can just nock an arrow and then walk off and get a soda or something.
This is a lot easier to show and do than it is to describe.