One of the methods usually given for working with complacency is to reflect on death, to understand that we may die tomorrow. That helps to bring up what we call a sense of "Samvega", a sense of urgency. Another technique for wanting to develop ourselves is to reflect on how the practice has already helped you, and that if we put forth the effort while we have the opportunity, realizing that we may die tomorrow, that it will continue to help us and to help others. Anther way we can lessen complacency is to develop the Compassion side of the practice more. Compassion is a great motivator. Reflect on Dukkha. Reflecting on Dukkha, especially the universality in the world and in ourselves and others, often will be a great motivator to not get complacent. As far as not getting the strings too tight, actually this comes from developing understanding that everything arises in time, and that we just continue to try to put forth the effort, reflecting on cause and effect, but it is an impersonal process. And from time to time, take joy with what we have already done, having Sympathetic Joy with our efforts, this brings more contentment.