Here is a trick to get a little extra edge at the blackjack table.
If you play against a skilled dealer who performs no more than two riffles and interleaves the cards evenly and precisely, have a look to see what happens to the aces that are dealt when they are scooped up into the discard tray. If many aces are put back into the discard tray with clumps of tens, you will find that in the following shoe you will get more blackjacks than you would expect mathematically. This is because the riffle action tends to leave initially adjacent cards together with greater frequency than chance alone would suggest. Not only will you gain from the fact that more blackjacks are dealt, but card counters will find high counts are more advantageous, since they depend for much of their edge on blackjacks. However, use your count as you would normally.
If the aces are mostly dealt in clumps of low cards, then the next shoe is likely to be disadvantageous for the player because aces are likely to appear with cards other than tens. Most of the value of an ace to the player comes from its being dealt with a ten. If this happens, it is a good idea to find another table if you can, rather than wait for a shuffle.
Some sophisticated players may get frustrated at this point and ask, "But what is my exact edge?" and "How many clumps of aces and small cards would have to exist to make the following shoe disadvantageous?" That knowledge is beyond the scope of this article. It depends on the exact riffling style of the dealer as well as the house shuffle, and requires the player to collect a lot of data on an individual dealer's style. Research is still being carried out on this subject; it may well be the last great art of blackjack advantage play.
Nevertheless, by following the simple instructions given above, you can only increase your advantage.