I've used several meditation apps including Headspace, Calm and Ten Percent Happier and found Harris' Waking Up to be by far the best. It separates itself from the others in that it speaks to the epistemological question of what it means to be a person.

Meditation is much more than simply clearing your mind or practicing letting go of your thoughts, although those are certainly benefits. It's about completely re-orienting yourself with respect to your relationship with the world and, most importantly, other people.