I got three, they all seem to work on me, but sometimes I prefer one over the other for no clear reason.
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Counting my breath duration. Breath in at normal speed, count how long it is, then breath out slower than that by two or three counts.
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Force my thoughts to become disorganised. I do something like free association between concepts and pictures of the inner eye. Common starting point for me is a free flight over a hilly landscape, then random things, woods, trees, rocks, water whatever, I don't try to control anything about the theme. If I start thinking coherently or about something concrete from my life, I just start again, with another nature scene.
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Imagine a calm scene. The suggested starting point I was told was floating on an air matteress in an alpine lake (helps that we know those around here, but I'm sure non-alpine lakes work too) and imagine the things you can see uphill as you drift around your axis.