PRACTICE. And practice some more. I find its easier to practice if the practice is in the guise of actual work or projects. Give yourself projects to do, see them through, and then move on to the next one. Over time you will get better and better. Just make sure it keep it challenging. Make the projects include stuff that you're not totally comfortable drawing, etc. If it doesn't come out perfect, or you're not happy with it, don't stress and give up, just know that's an area that you need to practice more in.
You'll be surprised at how much improvement you see if you just constantly work at it.
You'll be surprised at how much improvement you see if you just constantly work at it.