Every good general that goes into a war has a plan. A general would not haphazardly send troops into battle and make decisions on the spur of the moment. The general knows exactly why he is executing a plan and knows what responses from the enemy that he may face with each move he makes. The same is true of a good chess player. A good chess player has a solid plan to carry out in the game in order to achieve victory. Some inexperienced chess players though will stumble through a chess game looking for minor opportunities without executing an overarching plan.
If you threaten something here in one move and something over there in the next move your opponent will have an easy time defending against this attack. Your pieces have to work together to be effective. When you develop a plan your pieces can work in harmony. For example, you might plan to attack your opponent's king; one piece alone probably would not be able to do much, but the combined strength of several pieces makes a powerful attacking force. Another plan could be taking control of all the squares in a particular area of the board. Think of the chess pieces as your team and to be a good coach you have to use all of their strengths together.
A good general uses the specialized skills of his soldiers in a war and you should use your soldiers working together as well. Use the pieces for what they are best at, whether it is attacking your opponent or defending your king. Stick to your long-term plan and try not to fall into the trap of taking the short-term opportunities. Remember that you are here to win the war, not just the battle.