What can I do instead of this code to order (sometimes) simultaneous orders of drawing using same graphics object?

public FormTimerForDrawing()
        {
            InitializeComponent();

            Timer t = new Timer();
            t.Interval = 10;
            t.Tick += T_Tick; t.Start();

            lstDrawingOrders.Add(new drawingOrder
            {
                drawingOrderType = "RedLine",
                points = new Point[] 
                { new Point(20, 10), new Point(30, 50) }
            });
        }

        Graphics g;


        List<drawingOrder> lstDrawingOrders = new List<drawingOrder>();

        private void T_Tick(object sender, EventArgs e)
        {
            while (lstDrawingOrders.Count > 0)
            {
                switch (lstDrawingOrders[0].drawingOrderType)
                {
                    case "RedLine":
                        g.DrawLine(new Pen(Color.Red), lstDrawingOrders[0].points[0], lstDrawingOrders[0].points[1]);
                        break;
                }
                lstDrawingOrders.RemoveAt(0);
            }
        }

        class drawingOrder
        {
            public string drawingOrderType = "";
            public Point[] points;
        }

        private void FormTimerForDrwaing_Shown(object sender, EventArgs e)
        {
            g = CreateGraphics();
        }