Overclocking can damage hardware if u don't know how to do it right.
In your case for example (assuming that u have the GT version).
All is easy and safe .
Here is what u have to do.
First just run your favorite benchmark (3dmark 2006,2005 or 2003 for example ) and note the gotten result.
Lets take the example of 3dmark 2005
your result should be around 6000 points (depend on your processor and memory speed)
Then download ATI tools :
The software is ultra easy to use :
1) go to setting -->artifact scanning-->stop scanning .check this box and write a value between 1200s (20 Min) and 1800(30min). TO STOP Scanning after 30 or 20 min stable working
click find max core - watch your temp and note it -(do not go above 80c , 85c [red flag] , 60 (you have very good cooling) , 70 (your cooling is about right for the current clock) ).
Here ati tool will increase automatically your gpu frequency and check it for stability (artifact). then it will find the max gpu clock value
2)Click find max memory ...the same procedure.
finally to be completely artifact free lower the two gotten value (GPU, Memory) frequency by 10mhz .
Click --> New ---> then save
Your overclocked setting are saved in this profile if u want to load it automatically with windows start. then click setting -->start up -->check every time ati startes load ... select your new profile -->check load on windows start up.. select your new profile-->check when loaded via windows start up....
And your ok
Run again the benchmark and see your much your score is improved .
For sure u can overclock more but here u have to change cooling and do volt mod with don't worth the trouble for starter
If any question feel free to ask