Its probably best with Pokemon like your starter or Groudon just save before you get/battle them and if they are not shiny just turn it off and turn it back on and reload your game keep doing this until they are shiny be patient this may take awhile but you may get lucky and run into one in the wild in fact my little sister ran into a shiny Whismur and a shiny Lairon in the wild in her sapphire version she caught the shiny Whismur but the shiny Lairon got away.

its a 1 in a 8000th chance youll find one so good luck with that