Diagramming a sentence involves breaking it down into its grammatical components and illustrating the flow and relationships between them, as given below :
I
looked
↓
at
↓
myself in the
↓
mirror
↓
and saw
↓ ↓
you ↓
behind me
In this diagram:
"I" is the subject of the sentence.
"looked at myself in the mirror" is the main action or verb phrase.
"at" is a preposition introducing the prepositional phrase "at myself in the mirror."
"myself" is a reflexive pronoun, serving as the object of the preposition "at."
"mirror" is the object of the preposition "in."
"and" is a coordinating conjunction connecting the two main verbs.
"saw" is the second main verb.
"you" is the direct object of the verb "saw."
"behind me" is a prepositional phrase modifying "saw," with "behind" as the preposition, and "me" as the object of the preposition