Hands can be horrible to draw, and that inspired me to make a guide on how I manage to do them. This is based from working in FireAlpaca (www.firealpaca.com/).
Step 1: Parts of the Hand
Photo credit to Melyssah6-Stock on Deviantart, with my lines edited over it.
The first thing I note when drawing a hand is the 3D rectangle that forms the palm, the circles that show knuckle positions, and the lines that make up the fingers.
Step 2: Build the Frame
Start out by placing those building blocks in the pose you want your hand in. There is no shame in using references to decide where things should lie. I'm using a simple pose for this guide.
Step 3: Flesh It Out
Flesh out that skeleton of a hand. Fingers grow slightly skinnier towards the tip, and are broken into three segments. The top segment has a rounded tip as the finger ends.
Step 4: Give It Some Structure
Refine the shape of the hand by adding the ‘boniness’ of it. Fingers generally dip in towards the middle of each segment. Add webbing between the fingers.
Step 5: Add in Details
Add the wrinkles and tendons. Use the knuckles as guidelines for the tendons reaching down from to the base. The first knuckle on the finger has more wrinkles than the next knuckle. Define the nails.
Step 6: Basic Skin Tone
Lay down your base skin tone on a layer below your lineart. Recolor the lineart black using the "protect alpha" setting by the layers.
Step 7: The First Shadows
Lay your shadows. Use a color darker, slightly more saturated, and slightly redder than the base skin tone. I leave the top segment of the fingers shaded as this part tends to get flushed more easily.
Step 8: Blend Out the Shadows
Use your watercolor brush to blend out the shadows. Keep your color set on the color of the shadow, and follow the direction of your lineart when blending it out.
Step 9: The Highlights
Take a color lighter and slightly yellower than your base skin tone and lay your highlights. Add thin lines up the middle of the fingers to lighten them up.
Step 10: Blend Out the Highlights
Use your watercolor brush to blend out the highlights. Leave the color you're using to blend on your highlight color.
Step 11: The Darker Shadows
Take a color darker and slightly redder than your first shadows for your darkest shadows. Lay these darkest shadows out.
Step 12: Blend Your Darkest Shadows
Blend these dark shadows out using your watercolor tool. Leave your color on the darkest color shade.
Step 13: Starting the Nails
Use a color whiter than your base skin tone and color the nails in.
Step 14: Refining the Nails
Blend your base skin color down the middle of the nail using your watercolor tool. Add a whiter cuticle and nail tip to the nails.
Step 15: Reflective Light
Use the watercolor tool in the highlight color to add a thin reflection on the edges of the hand, between the shadow and the lineart.
Step 16: Coloring the Lineart
Recolor the lineart to a shade darker than the darkest shadow color. Around the lighter areas of your drawing (near reflections, for example), use the watercolor tool to color the lines a bit lighter.
Step 17: When It Comes to Palms...
When a pose shows the palm of a hand, its important to remember the palm is much squishier than the top. The red arrows show some straight, hard spots, and the blue arrows show some padded, round spots. I used the same method as before to draw this hand!
Step 18: REFERENCES
References are your best friend! It isn't cheating to use them, and you have two hands to reference in front of you all the time. References can not only help with lighting, but with color as well.