Get some friends together and talk bollocks every now and then and call yourselves the "Illuminati". That's essentially what the original crew would have done. You can also wear fancy jewellery and outfits if that sort of thing floats your boat. Just remember though that ultimately it's all meaningless nonsense.
That's awesome, But you'll have to be dead. The ILLUMINATI -- the real one -- was an enlightment society in the 18th Century. They sat, Drank, Ate, And talked philosophy and science. They also all died.
Current usage of the Illuminati refers to mostly fictitious entities or it is inscribed to other groups such as masons -- like the ring in the picture. The masons predate the Illuminati -- so there's a problem there. Perhaps you want to be a free mason?