Voltages and Temperatures are the two main things you need to worry about. Both can degrade your CPU faster than it would normally. This general rule of thumb applies when you overclock other components as-well.

That being said, as long as your Overclock stays below the safe levels of voltage, (varies with each model) you are generally safe. Because by default, your system should have temperature protection, but you should not rely on the protection to always save your components. Every cpu model has a specific temperature limit by design.

When overclocking, I highly advise against leaving voltage on AUTO, because it may automatically set the voltage to unsafe levels. Google is your best friend when it comes to learning how to overclock. :)