1) Look at guide line settings in the Work Environment.
>Work Environment, > User Preferences > Guide Lines.
Unclick the "fixed angle" option.
Look at the other options also as they are all very helpful or irritating depending on your goals.
2) search help on Snaps and Relative Construction, these will help you snap to 'imaginary" intersections and such.
3) Watch this great video by Eric Bobrow,
http://www.actemplate.com/video-tips/trace2d/
4) I love angels! Thanks for the lift!
Snap