by David Gate
A really nice little tip that I always give to my new users is the classic lines and arcs trick. Many people will create a line. Stop. Change Command and create an arc. Stop. Change Command and draw more lines.
Well you can do this all using the line command. After drawing your line, move your mouse pointer to the start point of your new line (the end point of your last line). You can then click and drag away from that point and create a number of different arcs. Perpendicular or Tangent ones in multiple directions depending on the direction of your drag.
See my little animation below to help explain this: