public partial class Form1 : Form
{
    delegate void SetTextDelegate(Control control, string text);
    public void SetText(Control control, string text)
    {
        if (this.InvokeRequired)
        {
            Invoke(new SetTextDelegate(SetText), new object[] { control, text });
        }
        else
        {
            control.Text = text;
        }
    }
}

public partial class Form2 : Form
{
    void button1_Click(object sender, EventArgs e)
    {
       form1.SetText(form1.textbox1, "hello");
       form1.SetText(form1.button1, "world");
    }
}