FireRed what do you do after beating Sabrina?

If you have not gone to Cinabar island, you just need to go there, get the Secret Key, and then you can defeat Blaine, the Gym Leader. If that is already done, then just go to Viridian city and go to the Gym there. Be carful, though. Giovani has very powerful pokemon. (not!!!!!) No need to thank me [:-)