Here's another good tutorial on adding chaos to your scenes in order to achieve a more realistic results. Also watch Photorealism in Blender: Unlocked if you're interested in this topic!
EJ 3D writes:
Basically in the video (which you should watch because I go into more detail) I just model some basic variations from the icosphere and the bezier curve for hair, and then use a particle system to scatter it on my object.
The biggest thing I discovered doing this tutorial was the material. Which is super simple, just a diffuse BSDF mixed with a transparent BSDF (which is completely see through) with a high factor so it is nearly fully see through. It creates a really nice look, especially with the hairs.
Anyway, I hope that helps you, and if you have any ideas to improve the material or the particle system (maybe using geo nodes?), comment below.