It really depends on the exact effect you're looking for.
"Cartoon" is a real vaigue description, theres about a million things you could do to a picture that would make it look "cartoony."
I say mess with some filters, mess with some blurs, mess with shadows and mess with contrast. After awhile you should get something you like.
Also get used to colorizing things.

But yeah, look around, you're sure to find something.

__________________