How to format my ipad
How to reset my ipad and delete all its content
Settings > General > Reset > Erase All Content And Settings.
If you have Settings > iCloud > Find My iPad enabled you will probably be prompted to turn that 'off' first
You've copied any purchases over to your computer's iTunes library via File > Devices > Transfer Purchases (you may not be able to redownload them all from the store), and copied off any important documents / photos ?