Think about a theme for your haiku and write down some of the words that come to mind on that theme.
Organize your thoughts roughly onto three lines. First, set the scene, then expand on that by expressing a feeling, making an observation or recording an action. Keep it simple.
Polish your haiku into three lines, the first with five syllables, the second line with seven syllables and the third line with five syllables. It may take some time and substitution of words to make it fit.