Oh wow. I love the darkness of this! Great shading and use of contrast, too. And all the details on Loki's armour ofcourse, those are amazing! You make it look like it's easy to draw while I think it's actually really hard.
Hehe, the hardest part is to keep going! You know when you start a drawing and suddenly you think 'I can't draw, why am I even trying this!?' And to keep going then, that's the hardest part. Well, besides getting the face right, if you're drawing someone who has to look like themselves, haha!
Do you use charcoal? Because otherwise my explanation might not work... But here goes: Not Smudging Use two pieces of paper (besides the paper you're drawing on). One for each hand to lean on and - this is important - do not let them move, lean your hand on it, but when you move your hand only move your hand - so do not drag the paper across your work. If you still have trouble with smudging, try working from the top left to the bottom right (reverse this if you're left-handed), this way your drawing hand won't go over any finished areas! And save the highlighting until last! Usually the only smudging trouble I have is after the drawing is finished and I have to handle it...
Really Black Areas save this until second last (last being highlights), start to fill the entire area - doesn't need to be really black yet. Now really blend it until it's smooth - use a tortillian preferably. Go over it again, this time trying to get it as black as you can (don't press too hard, you don't want to damage the paper), blend it again, with the tortillian. Now one more layer, this one you don't blend. And it should be black now!
Ah yes, highlighting is really important! I do it in three stages: 1. I use a cotton ball to dab away some of the charcoal (if you've used it before for blending you'll notice it tends to lighten things a bit). 2. For the more intense highlights I use a kneaded eraser. Make sure the edges are round, not sharp. 3. For the almost pure white areas or the really tiny highlights I use a sharpened eraser (just the normal hard kind).
For this I actually also used a tiny knife to add the highlights to the armor - because it was too small for the eraser. You just very carefully carve away the top layer of paper.