What makes an effective executive? The measure of the executive, Peter F. Drucker reminds us, is the ability to ''get the right things done.'' This usually involves doing what other people have overlooked as well as avoiding what is unproductive. Intelligence, imagination, and knowledge may all be wasted in an executive job without the acquired habits of mind that mold them into results. Drucker identifies five practices essential to business effectiveness that can, and must, be learned: managing time, contributions to the organization, mobilizing strength for best effect, setting the right priorities, and knitting all of them together with effective decisionmaking.