I would say that it will depend on what they want to do - but with Kat, have to agree: can only advise on what I've done:
Build AdSense self-hosted sites, sell affiliate products (to actual physical products) using Commission Junction, Amazon, etc., and freelance write.
Are they after a passive or active income? Does it matter?
Personally, as a writer, if they can get to learn SEO and copywriting, there's LOTS of money to be made - and NO END to the work!
Speaking of...gotta run...