actually,i haven't shaded the hair at all. its just lines.
for symmetry, i would suggest using a grid of 3x3 blocks.
use the grid on both reference and your blank paper.
now start drawing the outline; start from anywhere; use a scale if you have trouble concentrating on proportions. best thing to do is to use a grid of same size on both.
when I started, i used a calculator
but eventually after lots of practice you will not require any grid etc for the outline.
most importantly, don't give up if after one hour also your outlines don't look perfect. a near perfect outline will take you 3 to 4 hours.
realism requires time, patience, and lots of observation. best take a break after every hour, consult with friends to point out flaws. cause after just 3 hours into the sketch you might just start to go crazy.
another important thing is paper. your school notebook will not do.
but a sketch pad with paper of thickness of 100gsm or more. i use 130.
get pencils from 2h to 10b and also use .5mm 2b and hb for detailing.
a regular eraser and a kneadable eraser. kneadable erasers are hard to find but are the best.
try to find blending stumps for shading or make your own.
use a clear, big and detailed photo reference. shitty reference = shitty sketch.
try finding easy references at first
don't ever start with celebrities