There are lots of ways for doing it, this is just one of them.

Close your eyes
Relax, you're going to start a journey,
a journey back to the origins, your origins
ok
think of when you where born,
seems a like a long time ago doesn't it?
well, I don't think anyone remembers the day he was born but,
what's the first thing you can remember?
Give it a try, think, you got it?
how old were you back then? two years old? three? one?
This is gonna be your start point
Once you get it you can begin
Now the only thing have to do is to start remembering
Memories since you were one till now
Take your time, there's no need to rush through it
I like going carefully through each one
You might remember things, details, that had been forgotten
and every time you do it you'll find it difficult not to feel a certain happiness

This is something I do when I have a lot of useless time ahead, like in a bus trip of 2 or 3 hours and feel in the mood. It makes me relax and I really enjoy it.
Hope you find doing it interesting at least