As tight as you can go without it binding. If you spin the cranks (and wheel) off the ground, there should be no binding, no brrruping, no fluttering in the chain. Often if it's too tight you'll feel it when pedaling, particularly at speed or under strain.

If at that point you got more than the 1/2" play, you need to recenter your chainring, get a new one, or accept that your chain is dangerously loose. (I play this last game on my rain bike which has thrown me before and may do so again.)