In Shakespeare's Sonnet 14, some of the literary devices are as follows.
In line one, a metaphor is used whereby the speaker is like a farmer, plucking fruit (judgment) from an orchard (the stars). This gives the sense that the author picks from the heavens, as one would fruit.
Line two, "methinks I have astronomy," has metonymy:
Using a vaguely suggestive, physical object to embody a more general idea
The speaker intimates that he has a knowledge as of the heavens, referring to it in general terms as "astronomy." This follows the idea that some are able to read the heavens.
The next section is paradoxical in that having said he has astronomy, the speaker contradicts this with a list of the things he does not have, which would be ascribed to astronomers of the time:
He cannot tell of good or bad luck; or of outbreaks of plague or the kind of season will come ("harsh" winter, etc.), nor the future ("fortunes"), or the weather or how successful a prince might be. The speaker admits that in being an astronomer, he can do none of these things. (But we can expect a statement of what he can do since he infers that he is an astronomer...something else must be left.)
Line six represents a metaphor: "Pointing to each his thunder, rain and wind..." which suggests that he cannot foretell our personal troubles.... Once again, this line speaks of the poet's limitations.
Keeping with the idea of astronomy, the speaker shifts his focus in line nine and continues into line ten. This is a metaphor:
But from thine eyes my knowledge I derive,
And, constant stars, in them I read such art...
He derives his knowledge by looking in his sweetheart's eyes, which he metaphorically calls "constant stars," saying they have the same characteristics of stars: shining and bright. Here he starts to allude that he can read some information with this "astronomy," that "truth and beauty shall together thrive." And in relaying this, there is personification in that two abstract ideas such as "truth" and "beauty" will "thrive," which is a human characteristic.
Since "store" means to keep in reserve, one sources suggests a translation for line ten, “If from thyself to store thou wouldst convert,” means “If you would only turn your focus from yourself to creating a child…”
This lines seems like a paradox in that to create a child one must turn one's focus to oneself, not away from oneself. How can separating from oneself create a new life? The purpose of this line, though, may point again to the power "she" has, which the author earlier alludes to.
The last two lines, the rhyming couplet drive home the sonnet's most important point, and this is a metaphor related to "astronomy" as well:
Or else of thee this I prognosticate: [tell the future]
Thy end is truth's and beauty's doom and date.
If he is to tell the future, of this he is certain, that when she dies, that will be the doomsday, the death, of real truth and beauty. He is saying that no one is as beautiful as she, and truth reside more in her than anywhere else.
Because the imagery of astronomy runs throughout the sonnet, this is also an extended metaphor, where the original comparison runs throughout the poem (or sonnet). The purpose of the extended metaphor is to create a comparison and then refer to that comparison over and again to impart the poet's meaning to his audience more powerfully.