The most important thing is the temperature of your cpu cores and the die. First you need to know what the max. Temp of your Cpu is. After this you should get two important programs: Prime95 http://www.mersenne.org/freesoft/
and Core Temp http://www.alcpu.com/CoreTemp/
Prime95 uses Lucas Lehmer iterations to get your cpu cores to 100% load.
While doing this watch your cpu temperature in Core Temp. It should not exceed the max. Temp determined for your cpu.
It should be pretty difficult to overclock and stay at a reasonable temperature with just the oem heatsink and fan.
For instant overclocking i use AMD Overdrive
It allows you to make various changes and also has a 100% load program like prime95 and also can make a benchmark for your cpu. But after a system restart you have to start amd overdrive again because the changes arent saved to the Bios.
To overclock your cpu you have to make small changes to the multiplier and maybe to the vcore (Improve the multiplier first and run stability test. If it gets unstable improve the vcore a bit and test again). But be very careful with the last one as a too high vcore can damage your cpu. After a change make a run with prime95 or equal programs to look for system stability and temperature.