I've been getting requests from people a lot lately about drawing references, posing and various other things, so I will be posting them up here.
I had problems with hands for ages, and after reading several tutorials on them, I've learned to break it down into three points when sketching. "fingers" (treated as one entity) palm, and thumb.
The palm is simply used as a base point for everything else to sit on. it is round on the lower hand and more squared off at the top.
The fingers I draw them as one single "fan" shape, and from there I work out each individual digit. I find it easier to kinda square them off until I do detail work and from there the final shape.
The thumb is treated separately because I always felt it was probably the most important aspect of the hand. When looking at hands, you can almost instantly tell when something is off simply because the thumb was placed incorrectly or even on the wrong side of the hand. You can even leave the details of the other fingers off or obscured but so long as the thumb is more or less correct, most people won't even think much of the other fingers.
The only time this isn't true is during a closeup of the hand itself, and it becomes the focus of the image, and you have to pay close attention to details on the hand. The further away a character's hands are from the 'view" of the image, the less details you have to put in for this.