Here are some meditation advises which I found useful, by Dharma
Dan:
If you can perceive one sensation per second, try for two. If
you can perceive two unique sensations per second, try to perceive
four. Keep increasing your perceptual threshold in this way until
the illusion of continuity that binds you on the wheel of suffering
shatters. In short, when doing insight practices, constantly work
to perceive sensations arise and pass as quickly and accurately as
you possibly can. With the spirit of a racecar driver who is
constantly aware of how fast the car can go and still stay on the
track, you are strongly advised to stay on the cutting edge of your
ability to see the impermanence of sensations quickly and
accurately.
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These meditation objects and postures are not that important, but
understanding impermanence directly is.
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I sometimes meditate when reclining before sleep, when reclining in
the morning
before I have to get up, when I wake up in the middle of the night,
before catnaps on the couch, during boring lectures and meetings,
and in the lounge of the school I attend before afternoon classes.
I have come to the conclusion that five minutes of really engaged,
clear and focused practice in poor circumstances can often produce
more benefits for me than an hour of poor, vague and distracted
practice in optimal conditions.
Mastering the Core Teachings of the Buddha,
Adobe/.pdf version, by Arhat, Dharma
Dan