I don't think it is possible to give tips for finding one's voice; it's one of those things for which there aren't really any tricks or shortcuts, or even any advice that necessarily translates from writer to writer. All I can tell you is to write as much as possible.
Here's a little song I wrote You might want to sing it note for note Don't worry, be happy In every life we have some trouble But when you worry you make it double Don't worry, be happy Don't worry, be happy now