Dedicate your time to reading books about drawing, anatomy, and perspective. Also try to find videos to watch as those can be quite helpful to visual learners. Then study the industry, find out what they like and try to imitate those drawing styles. As you get better, you will develop your own style. At that point, you can start building a portfolio. Keep in mind that this is an extremely long process and will take at least a few years, so don't be discouraged if it takes a while to improve. Just try your best.
I think that people who earn a living from art have generally invested at least 5-10 years of preparation in one way or another.
People can make astounding progress in just a year or two if they become REALLY obsessed with art and apply themselves in the most productive ways, and give up all of their other hobbies and interests to focus on learning art, but the truth is that most people just want to be good at art without doing the work.
Take classes. Read tutorials, draw what you see in real life. Practice your butt off for thousands of hours, upload your work, ask for feedback in the deviation thumbshares forum. Use google searches and youtube. Study and work at it the same way you would work at anything you want to do well.
Earning a living with art generally requires at least a few years of VERY dedicated learning and some marketing ability.