Personally, if I have a good battery and the bike turns over reasonably fast, I just connect my timing light up as I would for a running bike and wait until it's at least a little dark in the garage so I can see the marks... actually, I have trouble seeing sometimes anyway and the dark helps me out. My timing light connects to 110v and gives more light than the one I had that connected to a battery, so that helps. In fact, I've even just connected the light and turned the shaft by hand at the points... slowly... and when the light flashes I check to see where it is reference the timing marks. That's always gotten me close enough for the bike to start.

I'm sure others might do it a different way, including using a continuity light, but my way works for me.

On my current bike I was simply testing to see if timing was even close, and found that my wires to the points were switched... 1-4 was firing when 2-3 should have been. That was very easy to see and fix. The bike just backfired until I switched the wires, then it started after switching them.