If you've never seen a pokemon before and aren't sure if it's shiny, check for a ding and 2 stars that flash around the pokemon when it first comes out. This denotes a shiny. Some shinys are almost the same color as their normal counterparts, so the stars and sound are a givaway. In my entire pokemon playing time, I've only encountered 3 shinys, 1 in crystal (can't remember which, but not the red garados), a Zigzagoon in Saphire and some pokemon owned by a trainer in LG (waaaaaah). As stated below, it's not a matter of time, but a matter of luck. You might even run into 5 in a row if you are very very lucky.