I'm an aspiring artist myself, and here are some of my tips.
- Don't focus on drawing one thing. I did this, and now I can only draw canines at a decent level. I regret it every time I try to draw something new, so try to draw new things every day, even still life, even animals, even humans. Do a study where you look at photos and trace (yes, I did just say trace) them. It will help you learn proportions and anatomy. Then look at photo references for your art when you can.
- Don't use pure black or white for shading. Nothing in nature is ever pure black or white, so add hues of blue, green, red, etc in your shading. Also establish a light source before you start, it'll make it easier to shade.
- Don't try to develop a style from the get go. Try to go for realism. That was another mistake I made, and I regret it too. Make your figures as realistic as possible and the style will come after.
- Practice on paper first. Trust me, its easier. I do all my sketches on paper still.
That's about all I can offer. I really look forward to seeing your art progress!