[RajatPawar]

If a player is new - that means he's just registered. Add whatever you want to do after that!

pawn Код:

public OnPlayerRegister(playerid)
{
         register_player_account(playerid..);
         Do_Whatever_with_him_because_he's_new( playerid );
}

Because obviously - a player registers only once! (Unless, a faulty login system)