Alex, as far as where to start, find a Pokemon you like, and go for it. Search to your hearts content. I am currently in possesion of 2 RuSa shiney Pokemon, a Whismur and Numel, which are now fully evolved Exploud and Camarupt.
As far as Cradily goes, you can try saving right before you pick up your Cradily. Each time you reset you get another chance at it. Or you can just hatch eggs for it. Either way will be time consuming. I reset my Ruby game for over 6 hours and never got a shiney Mudkip. I temperarily gave up, but will go back once I have a new round of TMs from Ruby and reset again.
Kyfogre22, I thought Shiney Dusclops was red?
I am currently hoping to run into a shiney Sableye. Once I get there in Ruby, I will also try my best at a shiney Beldum, it looks so sweet..... Any shineys that get in my way will be caught as well....