Tactics are your carefully planned actions for attaining a certain goal. You'll have to come up with some clever tactics if you're going to figure out how to build the fastest race car and win the Girl Scout troop competition.
Tactics also refers to a branch of military science that deals with planning maneuvers. Military tactics involve organizing troops in certain ways, in various locations, and deploying them according to plan. Your military strategy is your plan of action to achieve your overall goal — sinking the Spanish armada, for instance — while your tactics are the nuts and bolts of how you achieve it — deploying small, agile gunboats. Tactics comes from the Greek root taktos, meaning "ordered, arranged."