//instance
private static ClientsListFormFluent instance;
        public static ClientsListFormFluent Instance
        {
            get
            {
                if (instance == null)
                    instance = new ClientsListFormFluent();
                return instance;
            }
        }

//mainform fluent
 if (!MainContainer.Controls.Contains(AssistanceListFluent.Instance))
            {
                MainContainer.Controls.Add(AssistanceListFluent.Instance);
                AssistanceListFluent.Instance.Dock = DockStyle.Fill;
                AssistanceListFluent.Instance.BringToFront();
            }
            AssistanceListFluent.Instance.BringToFront();