got same problem i haven catch any shiny pokemon l(
but my record is 33 skittys lol...
o yeh and i can change pokemon while im in the grass?
Well, you can change Pokemon, but it'll reset the counter (back to 0...). So it's not advisable really.
The main thing is patience. It can take some time. I usually do it bits at a time - chain for half-an-hour, take a break, maybe even come back the next day or so. Take the time, and if you are not sure about a patch, don't go for it, just reste it after 50 steps.
Also - never step up (your big fat head blocks the patch above you...), and don't go for patches on the side - only go for patches that are surrounded by others in all directions. (e.g.:
xxxxxxx
x
xxxxxx
x
xxxxxx
x
xxxxxx
xxxxxxx)
The x's represent one square each. Pretending that that is the entire patch of grass, only the orange ones should be gone into, as otherwise the chain may break ont he side, more often in the corner ones.
Above all, patience, also plenty of repels (stock up!). It pays off - I 've got quite a few shiny Pokemon in this way (including those elusive Eevees :) ).
To start off, try maybe having a lead Pokemon with the Ability Static (it can be fainted, as long as it leads the party), and try chaining some electric type Pokemon (like Shinx). The likihood of Electric types would then by higher, and thus easier to chain.
Also, there are some good guides and info on Serebii Forums - look around in the dp section there. :)