//Escrevendo o pacote
SocketPacket Packet = new SocketPacket(PacketID.AccountID);
Packet.WriteString(Username);
Packet.WriteString(Password);

Client.Socket.Send(Packet);

//Lendo o pacote
switch(Packet.ID)
{
 .....
    case PacketID.AccountID:
         string Username = Packet.ReadString();
         string Password = Packet.ReadString();
 .....
}

public class AccountPacket : IPacket
{
   public string Username { get; set; }
   public string Password { get; set; }

   public void Execute()
   {
      ....
   }
}