UPDATE:
I took the TOEFL a second time a couple of weeks ago, and I got 118! Reading: 30, Listening: 30, Speaking: 30, Writing: 28. Of course, I'm very happy with this score and I'm glad this is out of the way. In the end, I didn't practice the writing section a lot more than the first time. I just tried to memorize the essay structure given as an example in the official ETS preparation book. One more thing: don't be afraid to retake the TOEFL if you think you can do better, unlike the GMAT it is possible to choose which score you want to send to the business schools you're applying to.
Good luck to all of you!
Now the real fun begins, it's time to start studying for the GMAT...