I remember the first time using my pen on the bamboo. I was all shaky and couldn't get used to watching somewhere else (my screen) then where I was actually drawing (my tablet). But it got better! And so it will for you.
Now I'm not going to go too deep into how to improve your drawing in general. It's already quite good. But as goes for everyone, keep drawing a lot, lots of figures. Don't try to make them finished, just doodle around, make lots of drawings. I sadly don't recall who to give credits for this quote, but someone once said; everyone makes thousands of bad drawings in their life, the sooner you get them out the better. Someone already pointed you at Andrew Loomis. Another great instructor is Bridgeman's Complete guide to drawing from life. There is plenty of it on the internet
Then regarding to your question, how to improve the digital aspect. At first, it's about getting used to your tablet. After that, it's about getting used to your program. I strongly prefer Photoshop, but there are plenty who prefer Painter or Sai, or even ArtRage or GIMP. Get your own workflow, get brushes you like working with. This is only a small part of getting better at digital painting though, as most, if not everything, depends on color, value and composition (and a bit of brushwork). This is as much as a traditional things as it is a digital thing. A great place to learn this, at least I found it to be very useful, is ctrl + paint: [link] Another method I like to use, as I don't have access to art teachers, is to collect paintings you like and try to copy them. Not completely, but try to channel their style. You will notice that with drawing it, you will understand it a lot better then when just looking at it. Don't do it too often though! Your own work with always be worse looking, and you need paintings with which you are happy with too!
Hope I could help, and definitelly check out ctrl+paint!
Well, I got one good tip for you son: Don't draw on a paper with lines. Draw on a paper that's completely blank and neat. Your style and technique is already pretty good, but that you're not drawing on clean paper totally messes up the whole piece. :/
My recommendation would be to start studying things like shapes and simplify complex objects (example being...the arms are cylinders, the head is a cube/sphere). Draw geometric shapes from perspective, and arrange them into human figures. Once you've got the hang of that start learning how light works on simple/easy shapes. If you can realistically shade a cube or sphere, then you can shade pretty much anything.
Andrew Loomis has a lot of books available for download for free out there that are pretty much a beginners bible. I've been working pro for about 2 years now as an artist and I still refer to them a lot!
How can I improve my drawing is a pretty big question. Your going to get alot of what artist, my teachers, and peers said, is to draw constantly, research and meditated on art fundimentals and foundations, and get inspired.
Color theory, value, proportion, anatomy, and figure drawing are probably the important stuff for character design, but learning all of them counts and helps. If you learn anatomy and study figure drawing, these are the tools to help construct the figure. There is alot of ways of doing it.
Get GIMP and draw war. The reason I would recommend drawing battle scenes in particular is not so much motivated by a particular warlike personality but rather because such scenes are deeply rooted in a fantastic array of techniques: they will teach you how to draw people, movement, action, light effects, drama, emotions etc.
Scenes from regular life will appear still, fixed and motionless. You rarely see the kind of conglomerate of action in real life as you do in battle-focused art (compare drawing plants with drawing tanks in action).
Looking at your current art style I'd say you might want to look into SAI program instead of Photoshop. SAI moves more "naturally" to what you have experienced with a RL pencil and paper. It's free for a 31 day trial to see if you like it. Honestly, SAI+Photoshop is a strong program combo for digital arts.
Moving forward is just a matter of practice and sticking to it. It's only your first day, don't worry the results are not an instant masterpiece. It does take some time to learn your new tools and the tricks of Photoshop. In other words keep at it and you'll find yourself improving as you go.
It looks like you got shading down so you could also look into the world of color if you want to challenge yourself that way. Here is a really good guide to color (honestly better than a lot of art teachers I've had): [link]