start with the easy ones,such as the poetry of william carlos williams.
first of all,get to know the background of the poem and the introduction of the poet.
second,try to master some basic elements about poems as well as the old english if you're doing poems round 19th century or before.
third,enlarge your vocabulary.
fourth,broaden your imagination while appreciating.
last but not least,just like what stormsue said above,keep reading and practising and you will get the essence sooner or later.