Use the taper brush to sketch out the picture.(name this layer as sketching layer NOTE!:all other layers should be below the sketching layer.
Create a new layer below the sketching layer.Name it as base colour layer.
Tap and hold on the colour tab and move your finger close to the picture to find a neutral colour of the skin.
Use the round brush to apply the neutral colour around the face of the sketching u have done. NOTE!the colour should be applied on the layer below sketching layer. i.e; neutral colour layer.
Use your eraser tool to clean up all the part of colours u don't need.
Create a new layer below,then turn of the neutral colour layer.
On your layer, pick-up your round brush and lower the opacity to 20-19%.
Tap and hold then move to a part of the picture u want to get the shadow colour.( There are 3 main shadows; 1.dark shadow 2.mid shadow 3.light shadow. And u can also have your highlights).
Increase the size of your round brush to 30-25 for a faster and convinient shading.
Then you can now shade the colours as u see them on the picture.
When you are done shading, reduce the opacity to 15-12. Then you can now blend the shadows together by picking colours and shading the immediate areas of the colour you picked.
I HOPE YOU GOT ALL THIS INFO RIGHT. AND I HOPE YOU ALL LIKE THE ARTWORK.