Your example is definitely not complex. It is very straightforward; there is no question about what is going on in your code. And, in my opinion, it is not very long. I like it.
That being said, if you have a lot of code that empties out multiple textboxes, you could be write a little method like this one:
void ClearTextboxes(params TextBox[] args)
{
foreach (var textbox in args) textbox.Text = string.Empty;
}
Then call it with
ClearTextboxes(textBox1, textBox2, textBox3, textBox4, textBox5);
Or if you plan to do this to every single textbox on the form, you could do something like this:
foreach (var textbox in this.Controls.OfType<TextBox>()) textbox.Text = string.Empty;
And you could do similar things for checkboxes and radio buttons, e.g.
foreach (var checkbox in this.Controls.OfType<CheckBox>()) checkbox.Checked = false;
P.S. If you really want to make your code easier to work with, I would rename those controls with names that are meaningful, e.g. instead of textBox1
perhaps UserNameTextBox
(or some other descriptive name). That would be a much bigger improvement than shortening the clear command code.