What are the basic elements and features of poetry?

It's hard to 'define' poetry and establish a set of fixed features, but there are some general tendencies and typical features which are more often used in poetry than other genres.

Examples of such are brevity, overstructuring (grouping, repeating,... certain elements and thus structuring, creating meaning), self-referentiality (poems draw attention to themselves, they refer back to elements in themselves), subjectivity (poems are read from the highly subjective point of view of the speaker), fragile aesthetic illusion (the reader has to re-center him/herself in the fictional world), etc.

Poems also use certain features to create meaning which are not normally used for semantic purposes in other genres, e.g. typography and phonolgy.