Let the dealer break when the dealer is showing a break card. Do not hit a breaking hand in this situation. When the dealer has a break card showing, double down on ten or eleven.
Never split face cards when a dealer is showing a high card. If the player is counting cards and the deck is rich in face cards, the split may be okay. Always split aces. Split low pairs like two or threes or sixes if the dealer is showing a break card. Forget it if the dealer is showing a high card. When the dealer is showing a high card, the hand should be hit almost all of the time. If the dealer is showing a low break card, let the dealer break.
Play third base when possible so as to control the dealers hit cards. This is true for sure the more hands you are playing at a time. This also prevents some idiot from sitting down and taking the dealers break cards. Never take insurance on the dealer having a Blackjack, it is a bad bet odds wise. Do not split higher pairs if the dealer is showing a high card.
Do not plunge bet when losing, it is a good way to lose more due to the bad run you are having. If the cards are rushing for you, increase the bet size after a win. If the dealer is hot, leave the table or at least cut your wager size. Press winning streaks and cut wagers on losing streaks. Do not increase bets when losing, all this will do is increase the loss amount.
Set a loss limit and a time limit for your play. When either is hit, it is time to quit for that playing session. This advise goes for most online blackjack games like roulette and poker games. At some poker sites you even have the possibility to set your session for a fixed time and a maximum amount to deposit per day to keep you in line. Over staying is a good way to give back your winnings. If a winning streak turns sour, when a third of the winnings are lost it is time to quit the table. There is no sicker feeling than being substantially ahead and giving back all of the winnings.
Look for tables where the players seem to be winning as the dealer may be on a cold streak. If most of the players seem in a good mood, and they have stacks of chips in front of them then this is probably a good table to try. Let the dealer have the break card.