I have heard many people talking about how their arm should appear and their hand should look when shooting a bow lately. They then ask, how should the overall position of everything be. So here are some basic tips on how your hand position should be when shooting.
The idea is to have your hand (and by extension your arm) be more like a bar with a handle with your bow resting in your hand (the handle). Your hand position should on the bow should be with where you take your hand and when looking at your hand you should see your life line. That's the first line from your thumb going to the inside of your palm. In between that line and your thumb is the place the grip of your bow should sit.
Once you have that position of your hand and bow, next your thumb should be pointing at 2 o'clock (10 o'clock for lefty's) and then your index finger should be pointing at 10 o'clock (2 o'clock for lefty's). With that your hand should be at a 45 degree angle to your bow. That's the proper grip that you should have.
Now, at this point it is fairly hard to say, but once you have this, where exactly you put your fingers is totally completely up to you. So with that, some people are comfortable just extending their fingers (not really my flavor), some people rest their fingers on the riser, other tuck them into the little opening that is created with the angle. This part is completely up to you and what is the most comfortable and the most repeatable/consistent when shooting.
That's the idea, which is, so long as you have the basics down for keeping your hand position on the bow. Then, what happens next with your hand, as long as you keep it the same and consistent with every shot. Then, your arrow should leave the bow the same and be torque free (as much as possible), leaving you with a more consistent shooting and hitting your target where you want.