Elements of visual camouflage in rough order of importance: movement, shine, shape, sillhouette, color, shadow, spacing. As long as movement is careful, it don't shine, you break up the shape and don't sillhouette yourself on the horizon, color comes way down the list in things that draw the eye as long as it's not completely out of place. Using natural vegetation from the area that you're in is one of the the best ways to camouflage yourself. If the color of your clothing doesn't stand out too much, creative and effective use of vegetation and terrain are far more important than what pattern of camouflage clothing you're wearing.
Old deer hunter's trick: stand up and back into a medium sized cedar tree and you will virtually disappear, even if you're wearing blaze orange. You'll still be able to see out. You've covered movement, shine, shape, sillhouette color and shadow in one fell swoop.
Old duck hunter's trick: stand very close to a tree and you will be almost invisible to the ducks while still having a fairly wide field of fire. You've covered movement, shape, and sillhouette with the tree, shine and color with your camouflage clothing and equipment.
Just my two cent's worth.
Definitions:
Movement - self explanatory. Movement draws the eye very quickly.
Shine - anything can shine, including skin, eyeglasses, and rifle scopes, as well as any worn metal parts. Flashlights and cigarettes fall in this category, too.
Shape - the human torso, head, or the nice straight line of a rifle barrel all stand out.
Silhouette - allowing yourself to be highlighted against the sky. Also known as the military crest of a hill.
Color - self explanatory. As long as it ain't chartreuse or blaze orange, most dull colors look remarkably the same at all but short distances.
Shadow - if you're standing behind something but I can still see your shadow, I know somebody or something is there.
Spacing - less obvious, but humans often do things in nice, even patterns. If it ain't random, it ain't natural. An example would be a line of well camouflaged fighting positions spaced evenly across the terrain. Even if you can't tell exactly what they are, the even spacing is a giveaway that they're not natural.
Haven't talked about noise discipline or smells at all yet.