Are there any tricks in this game that increase the chances of stumbling..

None that I know of at the moment. I would say looking for the Pokemon you want in double grass would increase your chances of finding one, but thats about it. If you feel like breeding for a shiny you can try the Masuda method. It changes your chances from 1/8192 to 1/2048. All you need is two breed able Pokemon from different countries. Though that still takes awhile. The quickest way to get one is by using an Action Replay. Though if you want a shiny legendary Pokemon you can soft reset for it if you save before battle. Anyway though double grass is most likely your best bet for a wild shiny since I think where some people are running into them at.

To get a shiny Pokemon,you either have to breed Pokemon from two diffrent countries (UK and America Pokemon,for example or Japanese Pokemon and American Pokemon,it dosn't matter)and your chances are reduced.
For legandary Pokemon,save and keep turning it on and off until you get a shiny,then catch it. Or run around and hope you get one. I got a shiny magicarp once from fishing in Pokemon Emerald.

There is a 1 out of 8023 chance you'll stumble across a shiny pokemon. But, I know how to get this chance to a 1 out of 2048 (and I did calculate this really)to find a shiny. What you do is get a Pokemon that has the pokerus disease. Then take that Pokemon to a patch of grass and make sure you fight with that pokemon. It also helps to have that Pokemon at a high level. Another good tip is when your going to hatch an egg, save your game a couple steps before it hatches, and when it does, if it's not shiny, turn your DS off and try again. This will take a long time but if your lucky, then a shiny might hatch.