As you can see here , there are squares all on the sketch , why ? because I used grid sketching in order to make a perfect sketch . How do you do that ? Simple, get the picture you want to draw after, add squares using whatever program is in handy (I used MS Paint lol) then , on your paper, make the same number of squares which you have edited on your reference picture . Then sketch in each square individually , what this does is it reduces the working surface on which you have to concentrate , a bigger surface is harder to control . If you do each square really well then the sketch will be an exact match .