Well.......... to be honest, realism is not my thing. But I could give you some pointers about the making the general outline, if you'd like.
You might've heard this before, but start with geometric shapes. Monkeys are anatomically (comparatively) close to humans, so start the basic geometric shapes or a stick figure version of what you want your final product to be.
(E.g. a circle for the head, another circle for the mouth area/chin, curved line for the spine/limbs, circle for the hands, etc.)
Then just flesh it out, and this is just me, but I find charcoal easier to work with when I'm going for realistic. It helps out SO much with the shading part, but careful- it's not erasable.
