One good way to start writing poetry is to read all kinds of poetry: not just in order to imitate but to fill up your head with it, to absorb it, to make poetry an essential part of how you view the world.
Never forget that the subject is as important as your feeling; the mud puddle itself is as important as your pleasure in looking at it or splashing through it. Never let the mud puddle get lost in the poetry-because, in many ways, the mud puddle is the poetry.