A person who sometimes practices and sometimes doesn't has not developed a definite understanding of dharma
. Don't have a lot of projects on your mind, but do mind training single-mindedly.
From The Great Path of Awakening : An Easily Accessible Introduction for Ordinary People by Jamgon Kongtrul, translated by Ken McLeod. Copyright 1993 by Ken McLeod.
Published by arrangement with Shambhala Publications, Inc., Boston.
This site provides an on-line database of commentaries on the Tibetan Buddhist meditation practices of lojong (Mind Training) and tonglen.