Interesting question. Usually, people fantasize about time machines and time travel because of two reasons: 1) because they don't like how their life looks now and are imagining a better alternative through time displacement, or 2) they are immensely curious about time travel.
I happened to fit into both as a kid and have asked myself this question a few times throughout my life.
I have two sets of answers: one from when I was a child and one from when I was a teenager.
As a child, when I entered school age, all I wanted to do was to go back to the time when I didn't need to go to school and watch cartoons all day long. That was wish number one. And then, I wanted to go to a time when I was like my parents - adults who didn't need to go to school but weren't necessarily watching cartoons at home either. That was wish number two.
And then when I grew up and became a teenager, I wanted to experience the carefree nature of a child again. Wish number one. And then, again, I wanted to become an adult and leave start leaving my mark in the world. Wish number two.
These days though, I find myself wishing to go nowhere else but here, enjoying the present, not dreaming about any future or past.
So I guess if I find a time machine, I'll not use it, but pass it to someone else.