Fun fact: Do you know what the average winning hand in blackjack is? It's 18.5. Which means that, in the long run, 18 is a loser. And that brings us to our third mistake:
3. Not hitting a soft 18 against almost anything
Since 18 is below the average winning hand, it's in your interest to try to improve it whenever practical. I mean, think about it: When you have an 18, what hands can you beat? If the dealer has a 17, you're good. That's it. I mean, sure, you can win if the
dealer busts, but that doesn't make your 18 any better than a 16. Or a 12.
Since you're never going to hit a "hard" 18 (two 9's or an 8 and a 10, for example), the only 18 that it's really practical for you to hit is a "soft" 18...an Ace and a 7. "Soft" hands are so-called because the Ace can be played as either a 10 or an 11, depending on the impact of the next card you draw on your hand. A 10 or a face card landing on an Ace-7 gives you a total of 18, a much "softer" landing than if you were to draw the same card on a "hard" 18, which, as I mentioned above, surely you are never going to do.
You hit a soft 18 against most of the dealer's upcards for three reasons:
A. As stated above, 18 is a loser in the long run; it's below the average winning hand of 18.5. For the same reason, you never hit a soft 19 (Ace-8); it's a winner in the long run, since it's better than the average winning hand.
B. Most cards you can draw when hitting a soft 18 will either improve it (A,2,3) or leave it exactly the same (10,J,Q,K), so you have little to lose by taking a hit. This is another reason why we don't hit a soft 19: Only two cards can improve it, and most cards will actually make it worse.
C. You can't possibly bust when taking one hit on a soft 18, so it's a free chance to improve your hand when the dealer's upcard is a 9, 10 or face card, meaning there's a good chance he has you beat. It also means you can double down against the dealer's 5 or 6 without fear of busting.
There are three dealer upcards that you don't want to hit your Ace-7 against. If the dealer is showing a 7, you stand, because if he does have a 10 in the hole giving him a 17, you already have him beaten. Same if he shows an 8, which means you are likely to have a push. And you don't want to hit against a 2, just because the dealer's 2 is such a dangerous card; in the long run you're better off staying and hoping the dealer either busts or draws to 17.
Now go out there and make some money!