CURVES.
For some reason people seem to insist that hands are made up of straight lines.. fingers are parallel to each other (they are not), knuckles line up in a row (no) the edges of the hand are straight and parallel (nope!), Once an artist starts seeing the curves in the hands and thinking of them as flexible objects made of multiple parts, they quickly improve their hand drawings.
FINGERS
Everybody knows (or should) that the fingers are not all the same length. Our naughty middle finger is the longest, and the pointer and ring fingers along side are almost the same length (ring is a little shorter). The pinky is the odd man out, being much shorter. That of course forms a curve along the top of the hand. What is often missed is that arc of that curve is not just a function of the length of the fingers, because the knuckles are also curved. Pinky therefore is not only shorter it’s set farther down into the hand, giving it the double whammy. Ring finger is actually the same length as pointer, but it appears shorter because it’s knuckle is lower on the hand than pointer’s.
Likewise the pads of fingers are not the same size, and the creases that define the separation between the pads are very staggered. Pinky’s first crease (down from the tip) lines up with ring finger’s SECOND crease. The tip of pinky lines up with ring’s FIRST crease.
KNUCKLES
Each finger has three knuckles on the back of the hand. The main knuckle is located at the base of each finger. The two minor knuckles farther up toward the tip. The main knuckle is knobby and has tendons that cross it creating a corded look running up into the finger. The second knuckle is covered with a very circular wrinkled surface, and the smallest final knuckle is indicated with some horizontal creases. You would think the knuckles would line up with the corresponding separations between the pads on the underside of each finger, but you’d be wrong. Curl your pointer finger and look from the side… the second knuckle and the pad crease under it exactly line up. However the smaller upper knuckle is more forward on the finger than the crease below it. That’s nothing compared to the main knuckle. Here is where a lot of people get confused with hands. Open your hand and look at it palm toward you. Look at the base of each finger. Many people think the knuckle of the finger rests directly behind the crease that represents the base of the finger right under the bottom finger pad. Now turn your hand around. That main knuckle is SIGNIFICANTLY lower on the hand. In fact it’s below the upper pad of the palm that curve below all the fingers. A lot more of your finger resides inside the palm/body than you might think. Understanding that is a big part of figuring out hands”