Haïku tells about simple things, in a simple style, and with simple words.
Simplicity
Words
A
haiku becomes stronger by the use of simple words. They convey fewer connotations,
heaving the reader's mind freer. It is always important to ask oneself
if it is not possible to use a simpler word.
Style
A simple style, unaffected, without bombast, without the traditional subject-verb inversion. That seems to be valid only in the "Western " concept of haiku. The Japanese often use effects, bombast and inversions. However, those devices should not blur the images.
Always use the present tense in the "Western" conception. Although a Japanese haiku also uses the past tense, it prefers the present tense.
A haiku is small. To move the reader with few words, an excellent conception and a unique expression must be sought. However, one must take care to not complicate the style to the point where images lose their clarity.