Avoid taking risks when at all possible, and remember to avoid being too greedy and impatient as well. For example, if a boss is about to die in one more hit, but may be about to attack, wait until they leave themself open again rather than attacking then, because you run a good chance of dying otherwise and having to do it all over again. Also, avoid getting mad at the game if at all possible, because when it comes to Dark Souls, death leads to anger, which leads to more death, and therefore more anger.