Tennyson's use of figurative language heightens the power and meaning behind the words in the poem. I have selected two examples of simile and metaphor in which the connotation of the brings deeper meaning to the characterization and development of the poem.
Simile--Compares unlike objects using 'like' or 'as'.
The gemmy bridle glitter'd free,
Like to some branch of stars we see
Hung in the golden Galaxy.
Tennyson uses the a simile to compare the brilliance of Lancelot's ensemble to the stars; not only does he create dazzling imagery through this comparison, but the reader can also interpret that Lancelot shares other similarities to the "branch of stars" in that he is equally unattainable.
Metaphor-- Compares unlike objects without using 'like' or 'as'.
Tennyson compares the Lady's weaving to that of a "magic web," creating a spider metaphor. Like his use of simile, Tennyson's use of metaphor also brings deeper meaning to the text. The comparison of the Lady's textile to a web brings to mind how spiders use webs to trap their prey; however, in "The Lady of Shalott," the reverse seems true-- the Lady's web has entrapped her. Only in Part III of the poem does the Lady break free from the web of her own making and flings it away, but just as the spider depends on the web for sustenance and survival, so does the Lady; abandoning her craft brings about her eventual doom.