Hello Anon, and thank you :D Here is a walkthrough, hope it helps!
1. Here, you need not put in all the details like individual strands in your sketch/lineart. But best to have an idea of the general flow/direction of the hair, how round it is, etc.
2. I have a color palette set aside for each part; if I have three shades of color for the hair, this is where I use the ‘middle’ color
3. I use the darkest shade here. After deciding the light source, this is where I carve the hairstyle by detailing bunches of hair, following my lineart flow. Some might prefer going even more detailed and making thinner longer strands, starting from the hair crown.
4. Normally I end at step 3 and just add the highlights lol. But you can make hair more ‘juicy’ :3 Take the lighter shade now and add strands on the upper area (where light shines) which you haven’t touched with the dark color. I try to make the strands like fat leaves.
5. Also optional, you can add gradients and a little shine to make the color pop more.
6. Adding the white highlights and whatever touch-ups needed