For example never take insurance in blackjack or bet on any craps or any seven in craps. The house edge on hedge bets is always very high. If you are afraid of losing then don't gamble. There is no system that can beat a game of pure chance. There are plenty of charlatans promising systems that can beat games of luck like roulette, craps and the lottery.
Most systems trade a lot of small wins for a few huge losses.
In the long run it is impossible to beat the house at games entirely of chance. It pays to shop around for the best possible playing conditions. In many games, especially blackjack and video poker the rules can vary from one casino to another and one state to another. Know what rules are favorable to the player and seek them out. Avoid side bets and rule changes.