Q: what do I have to do to reset my mac for resale

See the post by rkaufmann87  Here...

https://discussions.apple.com/message/17309054

If you do not have the install disks, call 1-800-676-2775 nd give them the serial number, pay a shipping and handling fee.

If you have them, hold the C key while starting.  Use Disk Utility in the "install SL" to overwrite/ERASE (I would overwrite at least 7 times even though it takes much more time than simple erase).  Finsh the install up to ...

When it want to restart an ask for AppleID/regstering, simlpy power off and let the new person see that screen.

"C" key to the very best of my memory (been a while on that)

Also "option" held at startup will find the DVD as bootable in the disk drive (this one works for BootCamp, multiple boot drives, etc).

See Here  >  http://support.apple.com/kb/HT3910?viewlocale=en_US

This is also worth a look  >  How To Prepare a Mac For Sale

As AnaMusic points out, the articles-links in the thread she pointed to give detailed instructions.

I will remind that 7-pass erase should clear *any* personal (financial for example) data on the drive.

steve359 wrote:

 

Use Disk Utility in the "install SL" to overwrite/ERASE (I would overwrite at least 7 times even though it takes much more time than simple erase).

It is essential to use the security option to zero the drive, but seven pass seems excessive (unless you have had state secrets or something you shouldn't have had on the drive). Single pass should be adequate.