HD drawing question.

[Lilly]

I think the tool doesn't really matter that much here. Photoshops, GIMP, Paint.NET, probably even Illustrator and Inkscape could be used. I think many people draw on paper first, scan it and then "ink" and colour using such programs. Of course, the sketching part can be done digitally, too, but line control with tablets is often more difficult than with real pen&paper. You'd have the sketch on one layer, draw the black lines on a layer above, hide the sketch layer and colour on layers below the line layer (preferrably one layer / colour for these styles etc). Oh, of course you'd be using a giant canvas and paint zoomed-in (except for the first sketch, that obviously should be done with an overview of the whole piece; and be sure to zoom out and check consistency every once in a while).
The rest is pretty much knowing what you have to do. Anatomy, cloth folds, all that stuff requires practise and experience - drawing real-life objects is said to be more helpful for learning.

^ Second that to the max. This was my preferred method until I started drawing all my vectors from scratch in GIMP without using a scanned sketch. It's honestly quite time-consuming to carefully "transfer" your sketch into ink lines, but worth it for most character-only art, and if you're pretty familar with your tools and keyboard shortcuts, maybe an hour's worth of effort to do.

Although if I have to draw something digitally that demands a lot of detail, like with backgrounds, I'll save myself the trouble of redrawing every last little detail twice over and just do it all digitally in the first place. I've actually inked over a full paper drawing with a background before, it was a mind-numbing four hours of just tracing over the whole thing like a zombie. =P (And to think I had spent maybe five hours actually drawing the entire piece on paper! Ouch!)

Also, one really cool method is to ink your sketch traditionally, with an ink pen, scan it, and up the contrast in your art program of choice, and set white to transparency so it's a nice, clean ink layer. No vector tracing required, and you get the organic touch of the human hand in your inks! You can do something similar with actual sketches too, if you like that edgy feel to your art, which I actually covered in a tutorial I wrote myself on deviantART.

EDIT : Also, this is a pretty good tutorial if you want to draw art like this entirely with vectors, in programs like Inkscape and such. (Granted, it's about tracing over screencaps from MLP, something I don't really agree with, but it is pretty comprehensive about the use of Inkscape.) If Inkscape's too complicated, you can always try using Photoshop or GIMP's path tools instead; both of which are pretty easy to use, IMO.