Through sheer determination and much sober practice every day. While there are Buddhist philosophies which claim meditation is immediately perfect from the start (although I think that’s a metaphysical philosophical comment rather than a description of developed ability), I tend to subscribe more to schools of thought in Buddhism that consider meditation developmentally. If you want to learn guitar, you punish your fingers. When the barnacles of maddening boredom break off and the mind drops into unity, there is serenity. On psychedelics, this is the phase where the visuals turn into full blown visions.