Rule 1: Make a character that seems fun to play.
Rule 2: Within the constraints of Rule 1, make a character that does not do the same things in the same way as another character. Ideally, among all the players you should cover the four basic roles - defender, striker, controller and leader.
Shardmind is a good race for wizards, since you get a bonus to Int. Your second bonus can be Wis or Cha. If you choose Cha, look at the illusionist powers in Arcane Power (if you have access to that book); if Wis, look at powers that cause "save ends" effects, and the Orb of Imposition implement feature (and look at the awesomeness of your Thunderwave with a high WIS!)
Shardmind also works very well for psions of any flavor; it seems to be the race that was designed for that class.
An Int-Cha shardmind is likely to be hypnotic and glittery - although you look totally alien, you inspire curiosity and wonder rather than fear. An Int-Wis shardmind may be quiet and thoughtful, with a deep connection to the earth or to the planes.