It very much depends on whose opinion of "really freaking good" you're interested in. But, if you want to become a skilled artist, there's two parts to it.
The first part is technical skill. Some people have a natural ability to learn the tools of the trade, such as pencils/pens/paintbrushes, etc. But you must understand and practice with the tools. The next part is to retrain your brain in such a way that you can accurately reflect what you see with your eyes onto a piece of paper or canvas using those tools. Again, some people have a natural ability at this, while others must work hard at it. A great resource for this is the book Drawing on the Right Side of the Brain.
The second part is artistic intuition. Drawing a precise representation of what you see is called illustration. Drawing a personal interpretation of what you see is called art. It's taking what you see and changing it, ever-so-slightly or dramatically, based on your own unique perspective, so that others can see ordinary things in ways that maybe they've never seen them before. Some people have a natural knack for this. Others must develop it. In my opinion, this comes as a result of a lifestyle, immersing yourself in others' art, in a variety of experiences, and in a metaphysical sense, "getting in touch with yourself." It's hard to define this aspect, but it's one of the things that separates the good from the really freaking good.
People who create art with nothing but technical skill can get very good at illustration, but it lacks a spirit of its own. People who create art with a large amount of artistic intuition, but without the technical skill, are unable to form their artistic vision in a convincing manner.
On a broader scale, to get good at anything, you must understand HOW to be good at it, which is an ongoing process. If it's art, just start drawing and painting. Do it all the time, try out new techniques and media, and ALWAYS try to be learning something new. As time goes on, you'll learn new things and realize there are things you need to practice and learn that you weren't even aware of before. But one of the best ways to get "really freaking good" is to take risks. When you're afraid to try something because you think you'll fail, that's exactly when you need to forge ahead and persistently attack it until you achieve a level of success. Most people are too afraid of failure to push past the barriers that keep them mediocre.
Also, if part of your definition of success is making it into a career, garnering fame and money, one of the keys is to understand your audience's needs and meet them. If you can understand human nature and what people are looking for, and you can harness your honed ability to that end, and you experience a huge amount of luck, you can get that kind of success.