You Can Flash New Kennels For Making Tweaks To The Processor Etc(Over Clock To Improve Performance, Under Volt For better Battery)
You Can Also Check The wide Variety Of Custom Roms Such As Cm10.1 , Search Through The Xda Nexus 7 Android Development Page And SeWhat ROM Suits.
Firstly Though Create A nandroid Backup Of Your Current (Stock ROM) And Maybe Use An App Such As Titanium Back Up To Back Up Current Apps And Data