Pick a spot where you can write for a while without being disturbed. this could be a private spot where you are alone, or a public spot such as a coffee house or a park.
Begin by focusing on your immediate environment. Note the sights, sounds, smells all around you and start writing them down. As you do, let yourself get lost in your surroundings. You may want to to use apostrophe, or to shift perspectives.
After four or five minutes, turn your attention gradually inward to your experience of the scene—what it reminds you of or how it makes you feel, for instance. Don't try to control or direct this process, just tap into your internal language. And keep writing.
Now let go of the place entirely. Keep writing. Loosen your grip on the pen. Let your body relax, your eyelids get heavy. Write whatever comes.
As your energy wanes and you start to tire of writing, focus back onto the present setting. Take note again of the sights and sounds around you. Write them down briefly, even if they are the same ones your wrote down earlier, then stop.
When you've finished, put this away for at least a day, without rereading it, then take it out and revise it into a poem of between 15 and 25 lines. Theodore Roethke's "The Far Field" is an outstanding example of meditative poetry.