First, the very first line is an example of personification. "The poetry of earth is never dead." Poetry cannot be dead in the sense that humans die.
Also, in line seven, the poet speaks of the grasshopper having delight and fun. This is another example of personification.
Another example of personification would be in line ten and eleven in reference to the frost creating a silence.
The imagery is clear in line two. The poet indicates that the birds are feeling faint from the hot sun. The reader can visualize the birds about to faint from the hot sun.
The cricket's song in line twelve would be imagery. The reader can hear the sweet sound the cricket makes.
The poem is added below for easy reference:
The poetry of earth is never dead:
When all the birds are faint with the hot sun,
And hide in cooling trees, a voice will run
From hedge to hedge about the new-mown mead;
That is the Grasshopper's--he takes the lead
In summer luxury,--he has never done
With his delights; for when tired out with fun
He rests at ease beneath some pleasant weed.
The poetry of earth is ceasing never:
On a lone winter evening, when the frost
Has wrought a silence, from the stove there shrills
The Cricket's song, in warmth increasing ever,
And seems to one in drowsiness half lost,
The Grasshopper's among some grassy hills.