Hit on hard 8 or below. These are the hands that need 13 to make 21 and will not bust in case of a hit any way.
On a hand of hard 9 double against dealer's 3-6. This is the case when you are likely to win more money because the dealer is most likely to bust. As you have already 3 small cards on the table, the following cards in most cases will make you a good hand and bust the dealer.
Double on hard 10 against dealer's 2-9, otherwise hit. When you have a 10 you know that you cannot bust with the next card no matter which is it. The chances are high the dealer will bust as he will keep on hitting until 17.
Double on hard 11 if the dealer shows 2-10, otherwise hit. Use the odds of being dealt a 10 in your favor and maximize possible winnings.
Stand on hard 12 if the dealer has 4,5 or 6, otherwise hit. This is a hand likely to bust in case there are lots of small cards on the table. Therefore, hit only if the dealer has less than 4 and more than 6.
Stand on hard 13-16 in case dealer shows 2-6, otherwise hit. You probably already know that this hands of 13-16 are very likely to bust with the next card. Thus we recommend you to take a risk only if the dealer has over 6.
Stand on any hard hand of 17-21. These hands are VERY likely to bust when hit, that is why you should never risk.