At the very beginning of the act, the Chorus says,
Now old desire doth in his deathbed lie,
And young affection gapes to be his heir.
That fair for which love groaned for and would die,
With tender Juliet matched, is now not fair. (2.1-4)
In these lines old desire is personified, as it is given the ability to lie in a deathbed and die; further, young affection is personified as being ready to become the heir to old desire, which means that young affection is going to replace old desire in Romeo's heart. It is given the human quality of being an heir and experiencing anticipation. The beauty that Romeo's love groaned for and would die is personified as experiencing painful emotion and death.
Then, after Romeo runs away from his friends to scale the wall to Juliet's garden, Mercutio tries to compel him to return or at least confess his purpose. When Romeo does not answer, Benvolio tells Mercutio that
he hath hid himself among these trees
To be consorted with the humorous night. (2.1.33-34)
In these lines, Benvolio personifies night as something with whom one can consort, like a friend with whom one can be in league, and he also calls night humorous, another way of saying that the night is moody.
Hearing his friend, Mercutio, mocking him, Romeo then says,
He jests at scars that never felt a wound. (2.2.1)
Emotional scars cannot feel the wound that makes them, and so Romeo personifies scars here as being capable of such conscious feeling.
Further, when he sees Juliet upon her balcony, he says,
Her eye discourses; I will answer it. (2.2.13)
He means that her eyes seem to speak to him and he longs to answer them. Eyes, obviously, cannot talk in a literal sense, and so he personifies them by suggesting that they can.
He goes on to say,
Two of the fairest stars in all the heaven,
Having some business, do entreat her eyes
To twinkle in their spheres till they return. (2.2.15-17)
Romeo personifies the stars, suggesting that they have something other than shining to which they must attend, and so they beg Juliet's eyes to take their places until they can come back.