Indexing plugs ??

OK, new stupid question (and I'm too lazy to do search the net right now).

I always "assumed" that plugs would be indexed so the spark would face down into the cylinder, where the A/F mixture is coming up at it.

But now I have been told I want the spark to face UP into the valves.

A) Is this correct?
B) Should it be facing a particular valve? Intake? Exhaust?