What's the Way to clean out my mac ahead of giving it out?
To give it a full fresh and clean and welcome experience I would suggest you remove all stuff accumulated over time including all non apple aps.

To do that you can erase all the information from hard drive and simply reinstall the OS X.

Apple's knowledge base article has the steps: 


OS X Lion: Erase and reinstall Mac OS X - http://support.apple.com/kb/PH4439.


On most computers, the erase and install takes 30 minutes plus how ever long it takes to download the installer package from Apple's servers. That part is about a 4 GB download if you haven't saved it and follow the above instructions.