how to start a sentence off when describing someone?

There are many ways to describe someone, it's generally limited by your imagination and knowlegde of a language :) However there's a rule that when describing someone, start from the top. So firstly you describe head (or eyes, nose, mouth, hat, glasses etc., depending on how many details you want to describe), then torso (arms, chest, jacket, t-shirt etc.) and legs (analogically).
 
I know it's not exactly what you meant but I hope it will give you some clue :)

This is a compound sentence because it uses fanboys the s stands for since.