Personification is the humanizing of an inanimate object. In other words, it is the act of giving human traits to non-human things. Shakespeare was a master of this type of figurative language, and as such, his plays are absolutely riddled with personification.
It's difficult to choose just 3 examples of personification from "Romeo and Juliet;" however, there are a few extraordinary uses of it.
During the fight scene in the opening act, Prince Escalus admonishes the families for their constant fighting in the streets:
Three civil brawls, bred of an airy word
By thee, Old Capulet, and Montague,
Have thrice disturbed the quiet of our streets, (Act 1, scene I, lines 80-82).
In the same speech, Prince continues to speak figuratively, yet convincingly, when he warns (and foreshadows):
If ever you disturb our streets again,
Your lives shall pay the forfeit of the peace, (lines 87-88).
Later in Act I, scene I., Romeo laments to his cousin, Benvolio, about his unrequited love sickness. Love itself is personified in many different ways. Benvolio begins with:
Alas that love, so gentle in his view,
Should be so tyrannous and rough in proof! (lines 160-161).
To which Romeo responds:
Alas that love, whose view is muffled still,
Should without eyes see pathways to his will (lines 162-163).
His personified discussion continues through a string of juxtapositions:
Why then, O brawling love, O loving hate,
O anything, of nothing first create!
O heavy lightness, serious vanity,
Misshapen chaos of well-seeming forms,
Feather of lead, bright smoke, cold fire, sick health,
Still-waking sleep, that is not what it is! (lines 167-172).
Still later in Act I, scene II, Capulet and Paris have a discussion during which Capulet tries to convince Paris that his daughter is too young for marriage, and she is his only daughter, "Earth hath swallowed all my hopes but she," (line 14). He goes on to explain that he is hosting a party that evening and invites Paris to attend and take stock of the other beautiful girls who will be in attendance.
At my poor house look to behold this night
Earth-treading stars that make dark heaven light.
Such comfort as do lusty young men feel
When well-appareled April on the heel
Of limping Winter treads, even such delight
Among fresh fennel buds shall you this night
Inherit at my house, (lines 24-30).
Though these examples are early in the play, they illustrate Shakespeare's use of personification to bring the language to life.