Thanks for posting this references, they are wonderful! May i give some tips here?
One thing to say for starters is to not give up. Many people think in drawing more as a born talent, but is more of a skill, getting better with practice, and even if some people may have more hability in it, there is certain level of proficience wich is acessible to all. When begining, many people tend to force (press) the pencil. Draw soft (lightly) lines and only remake (reforce) the correct ones. Artists never get the draw right in the first strokes, they remake various times, correcting errors etc. in sketching way before make the finishing. Also dont keep making little strokes back-and-forth with the pencil (as if you were sawing a piece of wood). Just make a full movement, it desn't matter if is not correct - if you want to make a circle, make the full round move, even if the circle comes distorted - thats how your brain learns what you want and start calibrating your muscular memory (and that takes some - varying from person to person - don't worry). A good way to practice is copying the artists you like, thats how you get your influences. You'll note that even when you get good at it, your art is not equal to the original you were studying. That's ok for various reasons, both physical (maybe you are right handed and the artist is left handed etc.) or mental (your influences are different from the artist). Dont worry. You are developping your own style. Accept the way your body and mind works and improve on it the way you can. Art is not an exact science, with only one correct answer. And practice on paper, even if you plan to only work with digital drawing/painting. Some things you'll only learn when working on paper as the mind processes are sligthly different. Some people think the art should come perfect at first try, and that is biggest reason for frustation on begginners. If you done a sketch and you don'liked the result, just leave and use other part (or side) of the sheet, but just look at your sketch and try to see what you don't like first, and then try to fix that (but don't scould yourself, there's no need or use for that, you are learning, and thats how works). Think in drawing as sculping. You beggin with a crude block, start removing the parts you dont want and only add details in the end. There is no right or wrong way to do it, just the way you like, and thats the best way. Use cheap material in the beggining and only get expensive if you fell that you need it. Some good basic exercises to "calibrate" your hands: pick a sheet of paper, and fill with lines - horizontal ones, then vertical ones, and then diagonal - you can even draw one above other, it doesn't matter, just choose one direction and fill the page with full, soft moves, without worrying about making them perfect. Then turn the other side (or pick other one) and start filling with cicles (bubbles) of various sizes (even inside or above others), again, don't worry about getting them perfect. then pick another sheet and do the same with squares (and again don't worry about getting then sharp). The last one is a little complicated: draw a square, draw a cross inside of it , divinding at half horizontally and vertically, and then make a circle inside, touching the "walls" of the square only where the lines of the cross touch it. Again fill a sheet with various sizes and don't worry about mistakes. Also when doing that last one, you can keep cycling around the circle and then stop at one of the square divisions making an inside turn to the other division (like a bite in an apple), then do anothe full turn normally an when you reach the division just after the one you "bited", do it again till you complete the circle. Then, you can do all of these exercises on opposite direction - if you drawed the lines up to down, now do it down to up, if you draw the circles clockwise, now do it counter-clock and vice-versa - and then do all using waving lines (including the last ones changing direction). I know it sound silly, but believe, it really improves hand coordination and line quality/control. Wow, that was long. I hope this helps, altough is more theorical, basic stuff, i've seen too many people give up in the beggining, wich is really sad.