First he shoots Cloverfield on various digi-cams to cut costs -- he doesn't have to buy miles of film and pay for processing and digitizing (before editing), and the quality of the CGI can be lowered to the image quality that you get when you shoot digitally (especially if the imagery is supplied by consumer camcorders).
So, now JJ has the production costs down, how does he get the marketing costs down? Simple. Build a website and release stills once a week that will then be posted (along with a 200 word analysis) on the biggest movie sites -- free of charge.
Here's some analysis from /film entitled, in case it wasn't clear, 'Analysis: third photo revealed on Cloverfield website':
The original photo showed a close-up of two wide eyed fearful young women at 12:36 am. Some people speculated that the two women were actually the same actress. This has been confirmed false. She can also supposedly be seen in the trailer at the party. Some people claim they can see something in between their heads. A monster may-be? How about their hair and a street light?
I love that. It's like this was footage from an assassination. It's both in-depth and highly analytical -- we learn that the thing between the girls' heads may be either a monster or a strand of backlighted hair. Over at Monstermovieblog they're claiming analysis is impossible (but JJ still gets his still displayed, analysis or not). At Cinematical they're claiming nobody cares anymore:
Folks like to play games for a little while, but there comes a time when they tire of the mind-fu**ing and simply want to know the deal.
However, they take 376 words to establish that nobody cares (and JJ got more exposure for his still). And now you've read this piece which makes fun of all the free publicity JJ is getting in which JJ got yet more free exposure for his movie.
Hats off Mr. Abrams.