public void ShowMyForm()
{
    MyForm myForm = new MyForm();
    myForm.ShowDialog();
}

public void ShowMyForm()
{
    using (MyForm myForm = new MyForm())
    {
        myForm.ShowDialog();
    }
}

using ( var dlg = new MyDialog() )
{
    // other code here to initialize, etc.
    dlg.ShowDialog();
}