Mainly used three brushes to speed up the process of the work.

One with no opacity change only size, for easily flattening coloras and to draw.

A blending brush, this one has opacity on, and spacing of 25, you can also give the shape you want to this one to have a more paint effect.

And a spray brush for ultimate blending, didnt used spray before, works really great and speed up blending process, because you cant blend easy here in photoshop.

All settings to 100% opacity and flow

1.- Okay first part, dont knowwhhat ggig t o, s idraw a regulr girl and throw some sprays to see colors and how it will work, i leave cool color for the backgound agaisnt warm colors.

2.- I add another layer to start blending with the other brush, adding colors ging more form to the girl.

3.- started adding less saturated and dark colors to the pic to give more volume and detailed the face. I like so imerge the layer down.

4.- Added another layer Sprayed some blues, changed mode to overlay like it, erased were the girl is, merge it again, continue detailing.

5.- Didnt liked the floating bones, the sky was to simple added a cape for composition, like it so i merge it again. As you can see its easy to use flat color for the base and use the blending brushes to correct mistakes.

6.- Added a gradient on a layer to darken all the colors so you can notice more her face, to give deep, then merge it, started detailing, adding tiny details with a tiny brush adds more life to the drawing. like the chains.

7.- an the last one more details, when you got the idea the details are easier.

Combining the three brushes the pick looks more alive than just tryng to use one, like old works i have.

Probably with more details it will look cooler, but was just a kiriban exercise, i wasnt married with this idea just wanted to experiment, liked the lights and shadows.

A cool tip to know how the grayscale values looks, just create a new layer, fill it with black, and in mode put color instead of normal, it will substract all color from your pick, so you can close the eye to not see it, or open it to see the pick in blacks again, its a cool way that changing the image to grayscale, and easy to check your volume.

There is no science in photoshop, just read all the help topics and get tons of books, try to learn a trick each day, and later you will better each day.