Tactics
Your level of Tactics determines how much of your Base Damage you are capable of inflicting on opponents. The percentage is equal to your skill plus + 50% (for example, at 100 skill points you will deal 150% of your base damage, while a fighter with no skill will only deal 50%).
Instead of using Tactics to determine their spell damage levels, mages instead use the Evaluating Intelligence skill.
This skill is necessary to perform most Special Moves. It does not count toward lowering their mana requirements, however.
Training
Tactics can be gained anytime an opponent is hit with a weapon or fist. Once training of either Fencing, Mace Fighting, Swordsmanship, Archery or Wrestling is completed, Tactics will usually be very close or at the level you want. To finish training just keep fighting as you were.