Suppose if we are calling a form from a menu click on MDI form, then we need to create the instance declaration of that form at top level like this:

Form1 fm = null;

Then we need to define the menu click event to call the Form1 as follows:

private void form1ToolStripMenuItem_Click(object sender, EventArgs e)
{
if (fm == null|| fm.Text=="")
{
fm = new Form1();
fm.MdiParent = this;
fm.Dock = DockStyle.Fill;
fm.Show();
}
else if (CheckOpened(fm.Text))
{
fm.WindowState = FormWindowState.Normal;
fm.Dock = DockStyle.Fill;
fm.Show();
fm.Focus();
}
}

The CheckOpened defined to check the Form1 is already opened or not:

private bool CheckOpened(string name)
{
FormCollection fc = Application.OpenForms;
foreach (Form frm in fc)
{
if (frm.Text == name)
{
return true;
}
}
return false;
}

Hope this will solve the issues on creating multiple instance of a form also getting focus to the Form1 on menu click if it is already opened or minimized.