Best way to set the timing is to use a vacuum gauge while you're doing it. Some people can tune by ear but having the vacuum gauge telling you what's going on is much more reliable.
You can pick up a hand operated vacuum pump with a gauge at any parts store. It should have a manual that will get into using it to adjust your timing. If not, there's plenty of sites to google that have instructions for vacuum timing.
In a nutshell, you disconnect the vacuum advance and hook up the vacuum gauge to a manifold source. Start at something low and advance the timing slowly. As you advance the timing, the vacuum should increase. Once it peaks and starts to fall off, back it up until you're at the peak again. Then back it off 1-2 degrees and lock it in. Reconnect the vacuum advance and you're done.
While you're in there, you can also use the vacuum gauge to adjust your idle mixture too.