(Edit: This seemed like the place it would do the most good, though it may fit better under another forum. Please move if necessary. Thanks.)
Accurate drawing is the first key to representational, realistic art and illustration. The best approach to learning to draw accurately is through observational drawing and working from life using traditional materials in a traditional manner.
The principles, or fundamentals, are not many, nor are they complicated, but they are challenging to become proficient with, let alone master. Every piece of art starts and ends with the fundamentals. It is helpful to practice them both separately, to work out specific handling of the principle, and together to bring them all into one composition.
They take years to become proficient with, and a lifetime to master.
NOTE: This is just my little list and what makes sense to me.
At their most basic, and in order, they are:
Statement: Have something to say
Composition: Arrange it well so it says what you want it to
Accuracy: Accurate drawing of shape, proportion, perspective and form
Value: Careful observation and interpretation of shadow and light
Edges: Careful observation of edges of forms
Texture: Careful attention to the surface quality of the subject
Color: Careful observation or interpretation of color in the subject.
NOTE: There are many important secondary elements such as balance, rhythm, etc. but they fall somewhere under each of the fundamental princciples.
A certain natural heirarchy exists in representational art, though each subject poses some unique challenges. It is a bit difficult to put them in an order but suffice it to say that you need to be able to handle the more basic subjects very well before moving to the more advanced.
Basic Forms: sphere, cone, cylinder, cube, torus
Forms in Composition and Perspective
The Figure/Portrait in the Landscape en plein air
Good books to help with understanding and practice of these fundamentals:
"Drawing Essentials" by Deborah Rockman
"Drawing Scenery" by Jack Hamm
"Fun With A Pencil" by Andrew Loomis
"Figure Drawing For All It's Worth" by Andrew Loomis
"Successful Drawing" by Andrew Loomis
"Imaginitive Realism" by James Gurney
"Alla Prima" by Richard Schmid
"Elk Skull" - graphite - still life demo for class - 45 minutes