Quiet before bedtime—shoulderstands, slow movements, meditation rather than going to bed with reading or music or radio.
Affirm that this is what you want. Realize that it is going to take time. There is a crucial moment on waking up when you decide either to embrace the attractive stimulation of a new day or to linger in the night’s visions, write them down, recall them in detail.
Indeed, writing is a key technique. Begin to put one vague memory into words, and often a flood of related images will follow.
It takes time. You have to want to do it.