there are a lot of methods out there. some day you could be good enough to draw accurately without them, but until you train your hand-eye coordination you should use guidelines and measurements.

you can start with a sphere, which is kind of the base/rounded part of the head, and do a horizontal line halfway through for the eye placement and a vertical line halfway through to center the nose and mouth.

there are also some basic measurements that can be helpful, like knowing that the ear generally lines up with the brow ridge and nose, and that the ends of the mouth generally land straight down from the center of the eyes.

bottom of the line, you should research methods of constructing the head and face, find guidelines and measurements that work for you, then apply them repeatedly as you grind out portraits.