Milarepa often says there are many teachings in many texts, but what takes for meditation, for practice is to really think on the value of human life, and impermanence

The Dharma teachings has many many meanings, and many subjects. But, when it comes to real practice, then people lack ability to bring the mind to the main object, main things to meditate on, to think about. We can see the way of practicing that the great masters went through like Milarepa, and other masters. Milarepa often says there are many teachings in many texts, but what takes for meditation, for practice is to really think on the value of human life, and impermanence, and the shortcomings of Samsara and the benefit of Nirvana. Those things are very important, the most important things that one must meditate on. Otherwise, there is no improvement, no achievement through Dharma [practice].

 Hungkar Dorje Rinpoche, “GURU YOGA: The Source Of Power In Speech and The Purification”