Answer:
First off, you have to list down the qualities you like about your friend. Then, you find an object, event, or basically just anything. Make sure to compare them at the same level.
For example:
Compare your friend to the sun. What are their similarities? What are their comparisons?
Here's an analogy: My friend is like the sun that lights up my cloudy world. My friend's warm aura of love and care is like the sun's rays that envelopes my person in a sense of comfort. My friend is like an ocean with unknown secrets and deep trenches, barrier reefs of extreme beauty and creatures of magnifecence. My friend is like a chair where I go when I need rest, when I need someone to lean on.
My friend is... so on and so forth.