I decided to split my response to cover two topics
Using just your finger as described above. Draw a line from your elbow to the tip of your extended trigger finger.
You see a straight line. No angling the hand at the wrist. That is what YOU DO NOT WANT.
Point your finger 'quickly" toward the target, You're off to the left (if your right handed". You don't want your "elbow to the tip of the finger straight".
Cock your wrist a tad to the right (assuming your right handed). Now point at the target "quickly". You now notice its easier to point at the target, not to the left.
Try it, using a straight hand, and a cocked hand, see which one points at the target more naturally. Try it with the unloaded gun. You'll see the same results.
As to the grip it self. You want a firm grip, not a death grip. With a tight death grip you cannot squeeze the trigger without disturbing the aim.
A simple test to demonstrate this would be to take a small salt and pepper shaker set.
Draw a line on the table. Use one of the S&P shakers as the grip, the other as the trigger. Set them up on the line. Squeeze the grip shaker as hard as you can and slide the other with you trigger finger along the line.
Try the same thing with more of a relaxed grip. You'll notice its easier to keep the trigger shaker straight with the relaxed grip.
Sights on a pistol/revolver work the same way, use a firm but relaxed grip so the trigger squeeze doesn't disturb the sights.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071