Cloth...blender has a cloth simulator that can work pretty good. You apply it kind of like a modifier, and you can set an attachment point(s) too so that it follows whatever it needs to if it is on say a moving character or something.

Hair....if you are talking for a game, as in real time rendered, you would need to learn to create low-poly hair. From most of what I've seen, it tends to be some geometry that would represent "clumps" of strands of hair, not actual individual strands, as that is way too poly intensive for real-time generally. Then, you would texture it with something that well, looks like a length of clump of hair, preferably with an alpha channel, which means you don't see a quad group, rather a bunch of strands. And if you do it right, the structure can be kind of random(ish) as long as it somewhat flows with the hair direction.

Wrinkles, that depends on whether you want to paint the wrinkles, fully model them, or do a hi-rez normal map doing a sculpt. If you have the poly count available(as in you are on higher end systems) you could possibly literally model in some of the wrinkles. Sculpting tools can help, and generally sculpting doesn't HAVE to be with huge poly counts. Blender for example lets you use sculpt mode on models with any number of verts/tris, and it can either not add anything at all, rather you simply use the sculpting tools to move the verts, or it can dynamically add geometry where you sculpt. The second method will end up increasing your polys pretty quickly though. You can also paint wrinkles on just as part of the texture. How well it works depends on how much detail you can have/need, and how good you are at actually doing the texturing. The 3rd option I mention is the normal map. You create a high-rez version of your model, sculpt in all the wrinkles, etc.. that you need, and then bake that into a normal map, which you can then apply to your original model.

And I forgot to mention in the other post, I think when the poster is talking about cartoony character, he/she means something with a unique style. The anatomy wouldn't have to be perfect. The arms can be cylinders. The torso could literally be a sort of box if you wanted and that was the style, though the arms would also need to be more low-poly and boxy so the whole model fits that style. This method lets you have some anatomy differences in general, as in you don't have be perfect in the muscle structure for example. The head can have different shapes, elongated to an extreme, even boxy as well if you want. It would all be part of the style. And generally, these things require much less work to get right, especially since the word "right" is as you want it to be. The key to art and games like that is that everything be similar. You wouldn't put boxy characters in a world with realistic trees, rather trees made up of a simple cylinder truck with spheres for the leaves, etc...