use msi afterburner!and some benchmarking tool like 3dmark!
here is a small guide!
1.download and install above programs.(you don't need 3dmark!msi afterburner comes with a program called msi kombuster which is good for benchmarking!)
2.open afterburner
3.first overclock core clock by 10-20 mhz.
4.run kombuster and watch the heat levels!(keep testing for at least 10 minutes)
5.again increase the core clock by 10-20 mhz.
6.run kombuster again and test.
7.repeat 3 and for steps until you're satisfied with performanceor until you get artifacts.if this happens decrease the mhz by 10 and try again(usually msi afterburner won't let you increase your clock speeds more than what your card supports so you'll be fine)!and(watch the heat levels.at full load above 80c means death)
8.reset core clock and start with memory clock.
9.do the same we did with core clock.(again watch the heat levels)
10.after you get your memory and core clocks to satisfied rate this time we will do a full test with both core and memory clocks!this time let the test take at least 2-3 hours!if you get artifacts or bsod decrease both clocks about 10 and try again!
if you think the results are satisfying then save clock rates to a custom profile.(bottom middle bar)
when overclocking all you have to watch out for is excessive heat that the card generates!if you have a powerful cooling then it won't be a problem!if you have a stock cooling i recommend you to buy a new aftermarket cooler for your gpu!you'll atleast decreased the probability of frying your gpu that way!
and remember you're the one who is responsible for overclocking!if by someway you fry your card i'm or any other member is not responsible for that damage!that's why you should reffer to few online guide around the internet!overclockers forum is a good place to start!!also warranty will be void if you overclock so keep that in mind!
have a nice day bro!
cheers