In order of importance:
-A quality defender who can back-up the center and power foward spots. Get this through the draft, not a trade.
-A quality defending and slashing wing player. The better the passing skills are icing on the cake. Also grab this through the draft.
-A quality defending point man. This is a last resort. Passing and handle are mandatory but jump shot range past the three is not. Basically the worse his jumper the better he much be at defending, slashing, and passing. Again do it through the draft.
*If done trade Nate Robinson and some other pieces for either the wing or big listed above. Make sure the player coming in has no more than two years left on his contract or is under 27 and guaranteed to be one of the top 25 players in the league within the next three seasons.