ANALYSING A POEM

You may be asked to analyse ("appreciate" or "criticise" mean the same) an unseen poem out of context.
Here are some aspects you could comment on:
1) Topic and theme: the topic is the obvious subject (a vase of flowers) and the theme is the more abstract idea conveyed by it (the transience of life).
2) Speaker and audience: is there an evident personality or persona writing the poem and/or a specific audience?
3) Imagery: use of metaphor, simile and symbol
4) Verse form: sonnet and blank verse are the main types you should recognise. If not, note the rhyme scheme and rhythm.
5) Diction/lexis/vocabulary: notice any contrasts such as colour, the prevalence of a part of speech such as verbs, repetition, conversation, clusters of words with similar references, use of several monosyllables and overall register, whether formal or colloquial.
6) Sound effects: alliteration, assonance, onomatopoeia
7) Tone (irony etc) and mood (emotional atmosphere).
Always relate your findings to the local or total effect
A useful book defining technical terms is: The Oxford Dictionary of Literary Terms by Chris Baldick
Many are explained elsewhere on this blog.

Symbol

A symbol is an object which develops deeper meanings, sometimes during the course of a literary work. In "Lord of the Flies" the conch becomes a symbol of civilisation and order. Yet it is a "real" shell present in the narrative also.
In simile or metaphor the compared object is not real or present. If we speak of her "shell-like ears" there is no shell present in the discourse. Similarly in: "He retreated into his shell", there is no real shell.

METAPHOR

A metaphor compares two things which are not usually considered similar and finds something in common between them.  It does not use the words like or as.
Example: After the storm we were cocooned in our caravan.
The caravan is not a cocoon but it is warm, protective and cosy like a cocoon.
Some metaphors are so overused that they become dead metaphors: She is a bright girl. The girl's intelligence is compared to a light but it is not a fresh way of saying this.