How to hook up timing light and set timing on 77 chevy 350

This is a good procedure for use of a timing light.
One primary concern is safety as use of the light occurs with the engine running and puts parts of the human body near moving engine components.
http://www.equus.com/Content/Support/Manual/3551-55e.pdf

If you have points, set the dwell angle (Allen wrench), prior to adjusting the timing. Loosen the distributor mounting bolt and rotate the distributor to set the timing--counterclockwise to advance, clockwise to retard. Obtain timing degrees BTDC from a manual.