2. overlap lines slightly where they meet. this will keep corners from looking inappropriately rounded.
3. when sketching, don't "feather and fuzz" your way across the page - that is, don't make a vague-looking line out of many short, overlaping segments. instead, move your pencil from start to end in a controlled, fluid motion. you might find it helpful to draw a light guide line before drawing your final line. don't erase your guidelines when the drawing is complete - they will lend it character and life.
source: 101 things i learned in architecture school by matthew frederick