What are examples of metaphors and personification in Hamlet and how do they operate?

Personification appears in this line in Act IV, scene 1:

“Mad as the sea and the wind, when both contend/Which is the mightier."

The sea and the wind are here being personified as two angry men fighting to see which is stronger. This is an example of personification because the sea and wind are given human attributes of anger.

Here is one metaphor from Act I, scene ii: 

"This world...tis an unweeded garden, that grows...

Personification appears in this line in Act IV, scene 1:

“Mad as the sea and the wind, when both contend/Which is the mightier."

The sea and the wind are here being personified as two angry men fighting to see which is stronger. This is an example of personification because the sea and wind are given human attributes of anger.

Here is one metaphor from Act I, scene ii: 

"This world...tis an unweeded garden, that grows to seed; things rank and gross in nature possess it merely."

This metaphor compares the world, the court of Denmark, to an unweeded garden, thus characterizing it as a corrupt place, overgrown with 'weeds' (courtiers and possibly murdering uncles) that contribute nothing and choke out what is good and fruitful.

In Act I, scene ii we meet another metaphor: Here Hamlet uses the metaphor of his flesh melting into a dew to describe death. This expresses his wish at that death would be a form of disappearing, of nothingness, that would take away his pain. Later, thoughts of an afterlife in hell will disturb this pleasant image of dissolving:

O, that this too too solid flesh would

melt

 Thaw and resolve itself into a dew

And when Horatio speaks of the ghost as a speck of dust to irritate the mind's eye, he is saying that as a speck of dust in the eye is an irritant that won't go away until you do something about it, so the idea of the ghost will keep scratching and irritating Hamlet's mind until he does something about it. This makes a thought a physical attribute.