It was one of the most striking characteristics of Shakespeare's sonnets that he used simple, common, imagery in his similes and metaphors. This is in contrast to many of his contemporaries who were much better educated and liked to use imagery from ancient Greek and Latin literature and mythology. A good example of Shakespeare's simple, common, natural, unaffected imagery is his Sonnet #73, beginning
That time of year thou mayst in me behold
When yellow leaves, or none, or few, do hang
He is comparing his time of life, late miiddle age, to autumn--a perfectly natural comparison. Everybody knows what trees look like when their leaves all die and fall off. And probably most people have thought that the stages of life are like the seasons of the year.
In the next stanza Shakespeare compares his time of life to the twilight after sunset, something every reader knows, not from books, but from actual experience.
In the third stanza he compares his time of life to the glowing of a dying fire, something every reader has observed in outdoor fires and in fireplaces.
Shakespeare made a virtue of necessity. He did not have a university education. He drew his imagery from the world around him. This is what is most Shakespearean about Shakespeare.