How should I go about analysing an unseen text?

The most important factors to analyse in any text are form, language, and structure. Form refers to the medium through which the text is presented - is it a poem? A chapter from a novel? An autobiography? A play? All these contexts will effect the way we percieve a text - a play for example, is intended to incite certain reactions in an audience, whereas an autobiography will want to impart certain truths (or fictions) in its individual readers. Form also refers to the genre of the text - Romantic; Renaissance; comedy; tragedy, etc. Form is important for thinking about authorial intent.

Structure refers to the technical construction of the text. This can mean the length of the text, the way it is laid out (particularly in poetry, which may use varying stanza lengths or techiques such as enjambment), the chronological order of the text (is a plot interrupted with lots of flashbacks?), and the narrative perspective.

Language, of course refers to the words used. One should consider here whether the author uses formal or colloquial language, what techniques he uses to get his words to have a certain effect (for example assonance and alliteration), whether the language reflects a certain time period, and how far metaphor and metonymy are employed to create double meanings.

Also key when looking at a brand new text, is to highlight the themes raised in the text. Explore how these themes are expressed, how they move the action along, and how far they relate to the genre of the text. Always bring in any contextual knowledge you have about the author, time period or genre. Be sure to analyse how far the author's work is in keeping with the genre within which it is categorised, or how far it represents an innovation in that genre. Above all be sure to read both the text and the question carefully and fully, to avoid making any mistakes in the wording.