Tactics Handbook (Book)

Use training to your advantage. Avoid fighting more than one enemy at the same time. Be careful while chasing an enemy because you might get hurt by his allies or by other monsters and can't defend yourself while targeting him. Target only the closest enemy or you'll become confused and might not be able to defend yourself against other attacks.
Different enemies require different tactics. Some are better to be fought in an aggressive way; some should be fought in a defensive way. Which attack style you choose also depends on your equipment. If you wear only light armour, there is probably no point in fighting defensive and the other way around.