Looking at your own clothes or just clothes in general really helps! even if it isn’t what you’re trying to draw, it all helps in understanding how cloth things work. For flowy things I try to draw the ends loose, lots of curving on top of itself for big waves, keeping it a continuous wave. Sometimes I try and imagine the weight of the curve, how it fits in with the others... it kind of helps.
For anything with a large drop (skirts, capes, aprons) I tend to draw out an oval and edge lines to figure out the overall curve of the fabric and where it ends, then I go over with whatever curvy line looks nice and fits the base line. For the creases imagine there’s a point that everything is attached to…well there actually is but yeah, follow the peaks of the curves up to those points. Same goes for the bits of cloth folded over itself underneath.
In terms of animation a basic way of showing cloth is a wave. It’s a little hard to see here, but there’s a continuous wave to the right, the edge of the cloth rests on top of that imaginary line.
See more here.
Hair Cycle Animation
Usually I follow the same basics mentioned here with flowing cloth animations, where that kind of flowing/windy animation follows a wave form. I tend to do this by eye, but if it’s a bit hard to wrap your head around, making up a little wave graphic can be helpful.
Here’s a quick example (there’s one frame in there somewhere that’s bugging me…but it’s fine for the example). When I animate these sort of things I keep in mind how the invisible wave looks, and how whatever it is is being pushed. I do a lot of this in my head, so it’s a tad tricky to explain...
This is the animation slowed down, it moves very slowly at the base, moving to quick and tapering at the end as it’s pulled by everything else.
And slowed with a wave added. The wave doesn’t exactly fit…but I’ve just drawn it badly :\ in the case of short animations I tend to have things follow the timing of the wave in a very linear pattern, but it looks nicer with extra frames added to add some easing as it moves up or down. Having it suddenly skip ahead a bit can work well for rougher movement or when multiple things are affecting the movement.
Wave reference here.