best way to clean phone after new rom install

ive been away from the mod scene for a while but finally getting back in to it. quick question :confused:

whats the best way to clean a phone? i bought this opo off ebay and still has old users pictures and apps on it. its already rooted and i installed a new custom rom just today. do i need to wipe internal storage from recovery or does that wipe the os also? should i factory reset inside android? that used to be a no no :silly: