Why write a letter to yourself?
For one you can save on the stamp.
Most importantly, it’s good practice for writing to a friend. Alternately, you could write the practice letter to your friend and send a follow-up second version, but this time with different information, to another friend. Granted, that’s probably a second letter. But you get my point. Just like an appetite comes with eating, writing begets more writing and before you know it you have a pencil that’s worn down to a nub. Unless you’re using a pen, then it’ll eventually run out of ink. “There’s a lot of ink in that well,” as they say. Actually no one says that. But you know what I mean.