They are very difficult. If you have a weak mind and a weak body, you have weak principles. But don't lie, no matter how sweet it sounds. You tell only the sweet truth because he who speaks the unpleasant truth is a dead man. So, a weak mind means a weak body.
Meditation is dhyana, the seventh step in the ashtanga system.
After one step is perfect, then you take the next step. For dhyana, you must sit with a straight back with your eyes closed and focus on the bridge of the nostrils. If you don't do this, you're not centered. If the eyes open and close, so does the mind. Yoga is 95 percent practical.