I don't think that driver's question really got answered...

First off, you can avoid math in NL by flat-out refusing to call on a draw or when you think you are behind (unless the person bets near the minimum). That's not optimal play, but it's a decent way to play without ever doing math.

Next, memorize the major draw percentages. Basically, what you care about are that flush and open-ended straight draws make the best hand about 1/3 of the time after the flop and just under 1/5 of the time after the turn. That means you can profitably call 1/3 the pot (or less) on the flop if you will see both the turn and the river without having to call another bet. And you can profitably call 1/5 the pot (or less) on the turn.

If you have a combonation draw (flush + straight draw, or open-ended straight draw + pair, etc), then you are the favorite on the flop (don't just call - RAISE!), and you are going to win just over 1/4 of the time on the turn (so you can profitably call up to 1/4 the size of the pot).