How do I redirect to the previous action in ASP.NET MVC?

try:

public ActionResult MyNextAction()
{
    return Redirect(Request.UrlReferrer.ToString());
}

alternatively, touching on what darin said, try this:

public ActionResult MyFirstAction()
{
    return RedirectToAction("MyNextAction",
        new { r = Request.Url.ToString() });
}

then:

public ActionResult MyNextAction()
{
    return Redirect(Request.QueryString["r"]);
}