I'm trying to think of something helpful to say other than the usual (practice! use reference!) those are both true, but as far as more helpful advice???? Here's what I would recommend and see if it works for you? No shame if it doesn't, but some of these helped me a lot.
1) Look up some classic 1920s/30s era barbershop hair cuts and see if you can differentiate these as you draw them in your practice. I got a lot better at drawing "short hair" when I stopped treating it all as one category and instead differentiated between the various types of short hair cuts. Or do a different time period known for short hair cuts. Any time period before the 60s will probably give you predominantly short hair variations and can be helpful to draw from. Separating out a crew cut from a pompadour and a whole bunch of other styles helped me a lot. Or if you're thinking short women's hair, look at the differences between bobs and pixie cuts, maybe contrast the difference between a pixie cut in the 60s a la Twiggy and Audrey Hepburn vs the one Halle Berry had in the 90s/early 2000s.
2) for slicked back hair, the hair follicles themselves can often be pretty long, and probably will show more texture than hair that's cut short. So when drawing the texture, this will look less like a "blob" and have more distinct pieces that can be sketched. Slicking down hair tends to group and cluster follicles of hair together so that they look like chunky "pieces." For instance, look at this group shot from O Brother, Where Art Thou:
John Turturro's hair is barely distinguishable from his skull and has very little visible texture. Tim Blake Nelson's texture is mostly just visible in the bangs, where perspiration is making it stick into clumps a bit. And George Clooney has classic slicked back hair, with lot of structure and individual strands that would be super fun to draw! I would personally spend a lot more time distinguishing texture on him compared to the others. Anyhow, 1930s historical movies! Full of helpful hair!
3) make sure when drawing short hair (or any hair), you practice various textures from a wide range of ethnic backgrounds. Obviously, hair varies a lot both within racial groups, as well as across them, but drawing a "high and tight" style on stereotypical white, untextured hair feels very different than with highly textured, natural Black hair. And those are just two examples! Obviously, not everyone has hair that's "typical" of their ethnic background, but having a wide range of ideas about how hair can and does look helps a lot.
4) I read something an artist I like said recently of actually thinking of hair a bit like clothing, with folds and drape in it. This felt very true to me. Long hair will have more drape, like loose clothing. With short hair, it will be more revealing of the curvature of the structure beneath the hair, like tight clothing. In this case, the skull. Getting comfortable with drawing skulls/bald heads was big for me for getting to the point where I liked the short hair I drew.
Anyhow, that's my advice. I'm not an expert by any means, but some of these practices at least helped me get BETTER, if not perfect. Hope you enjoy your hair journey!
