new bool:Commands[MAX_PLAYERS];

//OnPlayerConnect
Commands[playerid] = false;

//OnPlayerSpawn
Commands[playerid] = true;

//OnPlayerCommandText
if(!Commands[playerid])
    return SendClientMessage(playerid,-1,"Please spawn before typing a command");

new bool:isspawned[MAX_PLAYERS]; //Create a variable that stores whether the player is spawned or not.

OnPlayerCommandText(playerid, cmdtext[])
{
  if(isspawned[playerid]) //Is the player spawned?
  {
     //commands
     return 1;
  }
  else return SendClientMessage(playerid, 0xFFFFFFAA, "Please spawn before using this command."); //Return that the player has to spawn if not.
}

OnPlayerSpawn(playerid)
{
  isspawned[playerid] = true; //If the player spawns, the value is set to true.
  return 1;
}

OnPlayerDeath(playerid)
{
  isspawned[playerid] = false; //If the player dies/despawn, the value is set to false.
  return 1;
} 

OnPlayerDisconnect(playerid, reason)
{
  isspawned[playerid] = false; //If the player dies/despawn, the value is set to false.
  return 1;
}

new CanUseCommands [ MAX_PLAYERS ] = 0;

CanUseCommands [ playerid ] = 0;

if( CanUseCommands [ playerid ] != 1 ) return false; // Put the rest of your commands under it!

CanUseCommands[ playerid ] = 0;

CanUseCommands [ playerid ] = 1;