There are several different positions where the dealer may flash the hole card. The seat you choose will depend on where the dealer is flashing.
Keep a very close eye on the dealer as they take their hole card. Watch every step from the movement of the deck and removing of the card to the actual tuck. Either you’ll see a weakness or you won’t. If they are following proper house procedures then you won’t. If you see any irregularities or deviations from the correct dealing procedures then you might have found something. First try to find out
when the dealer is flashing, then look for
where you might be able to see it.
Although sometimes you may spot a good dealer who has become weak due to the conditions. A tall dealer at a low table (or short dealer at a high table) will be uncomfortable and might introduce errors. Dealers with small hands or long fingernails might have trouble handling the cards. Sometimes jewelry like big rings or long bracelets can also affect their dealing.
In shoe games you can sometimes catch the next card, which will occasionally become the hole card if you time it right. This is more powerful because you will also know your hit cards.
See the thread on hole carding for more info:
http://www.blackjackinfo.com/bb/showthread.php?t=6051
-Sonny-