Many different rules and guidelines for writing haiku have been offered, attempting to capture the unique poetic effect of the form. Some haiku writers believe that you should only write a haiku out of what you, yourself, can observe out in the world. Some believe that if you write haiku you must use a word that describes a season. Some believe that a haiku must be stripped of much of the standard rules of grammar. More than any concrete rules, however, a haiku depends on the accuracy of the images and emotions it expresses.
The best way to begin writing haiku is to realize that haiku is made up of at least one concrete image. Images can come from your imagination or they can come from real life, or a mix of the two. Writing in the 5-7-5 format is the easiest way to begin. But don't be chained down to it! Many of the haiku masters whose work is displayed above don't use that structure at all!
The following are some tips from haiku poet William J. Higginson:
Is it brief?
Does it contain one or two clear images with no metaphors or similes?
Does the image, or do the images coming together create an emotion in the reader without telling the reader what emotion to feel?