Best way to clear data from Macbook Pro prior to selling ?

I have an old (2013) MacBook Pro that is no longer used. It was used for domestic use only so lots of personal data etc stored on it. I need to clear all this data from the system before selling it but have no idea what the best way is to do this. I assume there is a DIY method that can be used rather than paying an apple dealer to clear it ?

Suggestions appreciated.

Thanks

Brian.