I'm a seamstress by trade, and I've always found that knowing how clothing is constructed really helps me in drawing it on people.
For example, the coat you've drawn would have shoulder seams around the top of the arm, which will change the way the sleeves hang. Also, unless that belt were tied shut, the coat would hang straight down; it wouldn't cinch in to her waist. She also has epaulets (Those accessories on her shoulders.) If they are made out of metal, or even another kind of fabric, they're going to stand up a little, instead of following the drape of the fabric.
The fabric as you've drawn it now looks like a very thin costume satin because of all the thin, fine wrinkles. If it were made of somthing much stiffer, like leather, it would have only a few wrinkles, but they would be very stiff, prominent, and deep. Also, think about areas of stress and contraction, and draw in the wrinkles there. Think about
why the fabric is wrinkling there. Is it where her elbow is? If it's a leather jacket, wrinkles will remain visible even after she straightens her arm.
Here's a picture of how leather drapes. Notice that the most wrinkles appear at stress points, like the buttons and belt, (and shoulders, because it's on a dressform that's too big for it.) Leather is so heavy that any part of it not in direct contact with something, will usually hang straight down.
Start noticing these wrinkles every day with what you wear. T-shirts and tight tops will have more fine wrinkles and creases in more places than your jacket. A dress shirt will have more, deep wrinkles at the armpit, but hardly any on the chest when you stand straight. Notice where seams are in garments, and see why they're there. Some women's dress shirts have a dart under each breast to prevent the shirt from hanging loosely. Some shirts, like baseball tees, have a raglan shoulder seam, where the seam reaches from the armpit straight to the collar, instead of around the armpit. This makes more wrinkles at the armpit, but gives you a better range of motion for pitching and catching.
Whew. Got a little long winded, there.