What should i write to him?

So this boy lives far away and I want to write him a letter.. I really like him abd he's expecting a letter.. but I have no idea what to say, and I'm thinking about giving him my number. I want to make an impression on him but not come off creepy, ya know? And nothing cheesey. I'm stumped! Please give me some ideas? And should I tell him more about me? Thank you!