For beginners, colored pencil would be a better choice. They aren't easily erasable, just in case you believe you can erase it.
In spite of you being a fast learner, drawing still takes quite a lot of time to learn. The first way to start out is by learning gesture drawing. It helps you draw what you see, not what you believe is there. When I was in high school, the art teacher actually started us out with drawing toilet paper. Why? It was a simple cylinder that would have a random extra piece that would crinkle and fold, much like fabric.
Start with simple objects, and challenge yourself to do at least 1 complete drawing a day. Find a small box for a cube, maybe a potpourri cone for a cone shape, a stress ball for a sphere, and any can for a cylinder. Toy around with lighting by using a desk lamp and setting your object closer and further away. Try to pay attention to perspective by examining vanishing points. You don't need to become an expert, but doing theme days for each one will help you progress faster. Try a simple object first, then apply that to the fish.
For practice, try to use a 3B or 4B graphite pencil. Draw from your elbow, not your wrist. Investing in a table easel will benefit you. If you don't buy that, get a drawing board and lean it on the back of another chair. Having your drawings elevated allow you more freedom to work, and you will see your subject easier as you draw. It might seem like you can just lean your hand on the paper and draw well, but when you learn gesture drawing better, you'll find that it moves things along much faster. The finer details are done similar to normal writing.
Also, don't listen to the right-brain/left-brain junk. There is no such thing. My father, who is getting his doctorate in psychology, mentioned to me that discussing right-brained/left-brained things were actually a common joke among them. So saying something like, "Oh, I'm creative, I must be very right-brained," would be very tongue-in-cheek. Anyone with half a brain on either side can learn to draw, as long as there is an interest. The ones who "master" it are probably just more visual thinking than others. Those who think in pictures tend to communicate better that way.