As a kid I never found being told to 'be myself' was particularly helpful, it was too vague for me. Here's an A3 print with some pointers which any kid will enjoy reading on their wall.
It is sold rolled in a tube so will post safely anywhere in the world making the recipient smile. I can enclose a note with it if you want it posted off directly. Postage within Ireland is €5 everywhere else in the world is €6.50