First of all draw a circle.
Now draw these lines it'll help you to locate the area to draw eyes, nose and mouth.
Now start drawing Asta's face beneath the circle.
Now draw his eyes he has big eyes as you can see.
Now draw his nose and mouth.
Draw his smiling face at the end of the circle.
Draw his headband above the circle.
Now draw his hair he has rough looking hair. Some of his hair hanging down from the both side and between the eyes. And draw a series of spiky for his rest of the hair.
Now draw his neck and shoulder.
Now draw his clothes.
Now start drawing outline and don't forget to add a new layer for it.
Now remove the previous rough work layer.
Now colour Asta with white hair black clothes and headband and green eyes.