What's the proper way to minimize to tray a C# WinForms app?

There is actually no managed way to do that form of animation to the tray in native winforms, however you can P/Invoke shell32.dll to do it:

Some good info here (In the comments not the post):

http://blogs.msdn.com/jfoscoding/archive/2005/10/20/483300.aspx

And here it is in C++:

http://www.codeproject.com/KB/shell/minimizetotray.aspx

You can use that to figure out what stuff to Pinvoke for your C# version.

this.WindowState = FormWindowState.Minimized  

That is the built in way to do it and it looks fine to me most of the time. The only time is has some weirdness to it is if you call it on startup which has some weirdness sometimes which is why most people will also set the ShowInTaskbar = false and hide the form too.

http://msdn.microsoft.com/en-us/library/system.windows.forms.form.windowstate.aspx

It will helps:

public partial class Form1 : Form
{
    public static bool Close = false;
    Icon[] images;
    int offset = 0;

    public Form1()
    {
        InitializeComponent();

        notifyIcon1.BalloonTipText = "My application still working...";
        notifyIcon1.BalloonTipTitle = "My Sample Application";
        notifyIcon1.BalloonTipIcon = ToolTipIcon.Info; 
    }

    private void Form1_Resize(object sender, EventArgs e)
    {
        if (FormWindowState.Minimized == WindowState)
        {
            this.Hide();
            notifyIcon1.ShowBalloonTip(500);
            //WindowState = FormWindowState.Minimized;
        }
    }

    private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
        this.Show();
        notifyIcon1.ShowBalloonTip(1000);
        WindowState = FormWindowState.Normal;
    }

    private void maximizeToolStripMenuItem_Click(object sender, EventArgs e)
    {
        this.Show();
        WindowState = FormWindowState.Normal;
    }

    private void closeToolStripMenuItem_Click(object sender, EventArgs e)
    {
        Close = true;
        this.Close();  
    }

    // Handle Closing of the Form.
    protected override void OnClosing(CancelEventArgs e)
    {
        if (Close)
        {
            e.Cancel = false;
        }
        else
        {
            WindowState = FormWindowState.Minimized;
            e.Cancel = true;
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        // Load the basic set of eight icons.
        images = new Icon[5];
        images[0] = new Icon("C:\\icon1.ico");
        images[1] = new Icon("C:\\icon2.ico");
        images[2] = new Icon("C:\\icon3.ico");
        images[3] = new Icon("C:\\icon4.ico");
        images[4] = new Icon("C:\\icon5.ico");
    }

    private void timer1_Tick(object sender, EventArgs e)
    {
        // Change the icon.
        // This event handler fires once every second (1000 ms).
        if (offset < 5)
        {
            notifyIcon1.Icon = images[offset];
            offset++;
        }
        else
        {
            offset = 0;
        }
    }
}