Advanced phone customization/Overclocking and governors

Before we start,

Introduction

Overclocking is the process of boosting your phone's CPU beyond the rated speed, which can improve performance. Changing the governor gives you finer control on your phone's mechanism, potentially allowing you to choose between performance or battery life.

Governor

A governor is a series of settings that control how your phone controls the CPU. Your phone would have some default governors, which would often be named as

ondemand: supposed to be the best of both worlds - boosting performance during high loads - while dropping the clock speed otherwise to save battery life.
conservative: A battery-optimised version of onedmand
powersave: For the most battery life. Often drops the clock speed to the lowest, may also switch off some cores. Could make your phone unresponsive, be careful!

... and many more. Check the internet to find more about the quirks of some governors.

The difficulties

Often, you'll see that you cannot overclock beyond the maximum stock speed of your phone. In such cases, make sure that your phone is rooted. If that's already the case, you'll have to flash a custom kernel, which is out of scope for this guide.

But in some cases, you may instead discover that your phone has a hidden clock speed which you can easily activate!

Personal note: A Galaxy Grand Duos whose stock clockspeed is 1.2 GHz could be easily overclocked to 1.3 GHz by simply selecting the appropriate clockspeed within the app.

Procedure

Go to Google Play Store and choose your app. A good example is Kernel Tuner; there are more.
Open it. The app will mostly ask for root access, make sure that you grant it.
Look for a CPU option, and click it. Here you can modify the minimum and maximum clock speeds, and often overclock it if it's possible.
Look for a governor option. Here you can choose your governor (see above).
Test your overclock; look for a stress-testing app to make sure that you haven't accidentally set it too high.