SweetShark said:
Sadly for me, because most of the time I am at work when I am out, I don't have time to sketch even if I wanted -_-...
At least I can use my computer, like just now
Doesn't have to just be when you're out and about. Even at home, try to keep up your drawing. It's a practice thing, and the only way you'll get better is to improve and always be ready in case you have the urge to draw something.
But if you're at home with digital stuff - combine and layer colors, don't just go with one that you've created/found on the palette. Paint one color with a brush, then lessen the opacity and paint a different color over it. Do this over and over again with different colors. This has several purposes; one, it breaks up the color there, keeping the entire drawing from being exactly the same color - life's not like that. Everything's all different shades, tones, and mixtures. Skin has blue tints in its shadows, pink tints where the blood's close to the surface, yellow tints where it's not, highlights depending on the light in the room... You get the idea. Adding the different layers of color makes it both more interesting, and more realistic.
Another purpose here is to keep everything that you make a bit more unique. You might have added a bit more green in one drawing when compared to another, making a color that you don't normally use - that's a good thing! Learning's about doing new things, testing things, seeing if they work. If you find something you like, whether for the interesting effect or because it captures what's really there more accurately, remember what you did, and then work off of that with other tweaks. It's all a matter of trying new things,
The final purpose here is that it keeps you from using the standard 'burn and dodge' tools. Someone already mentioned it here earlier, but you really should try to stay away from using those as your shadows/highlights. Shadows are more than black or a darker shade of the earlier color, and the same for highlights with lighter colors. It's not accurate, it never quite looks right alone, and most artists can instantly tell you used dodge/burn because it has this overly-saturated, samey shading look.
I would like to agree with Eclipse Dragon. This is a wonderful topic; I've never really been a pen person, so the tutorial there was interesting and enlightening. ^_^