Answer: In dialog, cut out every instance of the word "I" that you possibly can.
We have a writer in our weekly group who has at least one "I" in every 20 words. It is the most annoying thing to read. We tell her every week how tired it makes us--I this, I that. You don't need it. "I" don't want to see it. Kill as many I's as possible.
Read the below blog, take notes, and do a google search for others:
You have a challenge. In a first person narrative, you cannot go back and forth between 'he said' and 'Bob said.' You can't say "Trevor said" since Trevor is the person telling the story. You will, therefore, have twice the challenge a third-person narrator has, to avoid taxing the reader with a single word "I" (he).
Fortunately, there are other writers who have sorted this out for you. They have figured out the tricks.
Find them online or in books. Read published first person narrative and take note. In the meantime, surf around and see how people handle this challenge.