Yesterday I went back running. I took my watch and realized that the chronometer was still set to 3h57m22s and the time still set on NYC's. I thought it was a good sign it was time to blog about the marathon.
This is not meant to be a comprehensive guide, I'm not an expert, but more a report about what I personally learnt about it and how I rationalized the whole process, with the hope it will be helpful and inspiring for somebody out there.
This is because I believe that the first and biggest contribution I can give is to share how an average runner like me could prepare and run those scary 42km. Because if I could make it, along with other 1 million people every year, I don't see why you shouldn't too.

The schedule is divided in 4 parts and you will need just from 4 to 6 months, about 4 days a week, from 30 minutes to 1 hour for each training. No big deal.
The schedule is planned for an average runner, somebody who's already running or doing some kind of sports twice a week, like playing football (soccer), swimming or riding a bike, and should help you finishing the marathon in about 4 hours.
I highly suggest you buy a watch with a heart rate monitor, it will tell you everything you need and will make the biggest difference during training. It will be like your silent training coach.
Remember to always do good stretching at the end. I believe skipping some exercises was one of the reasons of my injury. Each stretching exercise should last at least 1 minute, I've been told less is useless. I find stretching properly very rewarding.

The first part concentrates on gaining strength, it's a bit exhausting but it's also the less demanding in terms of time per training. As it puts a lot of pressure on your muscles and being at the beginning, you should try to avoid overtraining.
I know you'll say "it's not my case, I can try harder than the others". I did. And I got injured. I lost about one month and a half of training and some of the tonicity I had just gained with hard work. Just don't overdo, trust me.
Also, some days you'll not be able to follow the schedule because you'll be tired or just because you hit a bad day. It happens, don't insist.
The main exercise here is the repeat: this helps your heart gain elasticity, rise the anaerobic threshold and train it to recover under stress. It's pretty easy: your run at 80% of your possibility (it's not a sprint!) for 1 minute and recover another 1 minute at jogging speed, a bit slower than your running speed (don't walk!). My heart rate got to about 190 beats during the run and went back down to 140 during the recover. You'll do the repeats also in the other parts, but you'll run slower and for longer there. The recovering part is as important as the running part because your heart still works but your muscles recover. So don't walk.

A little legend: I considering the speed of running based on the heart beats (that's why the heart meter is so important). Your running pace should be below your anaerobic threshold. You calculate it like this: subtract your age from 220 and then calculate the 75-80% of it. In my case (220-29)*0.8=152. I believe it raised towards the end of the training to about 160.

• average speed: this should be your running speed during the marathon. You should be able to speak but with a bit of effort. (about 150 beats)
• good speed: this is a bit above the anaerobic threshold (about 170 beats for me). Speaking now is quite difficult.
• repeats (KxN minutes): means K times N minutes running + N minutes recovering: i.e. 2x2minutes means two times run 2 minutes plus 2 minutes recover (so 8 minutes in total).

Where not stated, there're always warming up and relaxing runs (i do 3km+3km). Warming up and relaxing speed was around 140 beats for me. As a rule of thumb, you should be able to speak without effort while you run.

My schedule was (16 weeks):

(Week 1-4)
Monday: 6x1minute repeats
Wednesday: 6km uphill (3uphill+3downhill) at good speed (I ran at 170 beats)
Friday: 6x1minute repeats
Sunday: 6km of running at average speed (I ran at 150 beats at this stage)

The second part is similar to the first one, but you'll start running a bit longer distances and do longer repeats. The repeats go to 2 minutes of running and 2 minutes of recovering. Of course you run a bit slower, you'll learn your limits.

(Week 5-8)
Monday: 4x1minute + 2x2minutes repeats
Wednesday: 3km flat and 6km uphill (3+3) + 3km flat at good speed, like before
Friday: 4x1minute + 2x2minutes repeats
Sunday: 9-12km of running at average speed (I ran at 150 beats at this stage)

During the third part you'll start running longer runs and train your heart on quantity, making it bigger:

(Week 9-12)
Monday: 3x2minutes + 2x4minutes repeats
Wednesday: 3km flat and 6km uphill (3+3) + 3km flat at good speed, like before
Friday: 3x2minutes + 2x4minutes repeats
Sunday: 12-16km of running at average speed (I ran at 155 beats)

The forth part is the last one, preparing you to the actual marathon. It's very important you run at least two long runs because apart from training your heart and muscles, you also have to train your body to keep energies and not release them to quickly. Keep in mind you'll run for 4 hours. Ideally you should have at least two of them, I ran half a marathon and about 32km during this time. Plan them accordingly, I ran the 32km 2 weeks before the marathon.

(Week 13-16)
Monday: 5x6minutes repeats
Wednesday: 12km flat at good speed
Friday: 5x6minutes repeats
Sunday: 18-22km of running at average speed (I ran at 160 beats)

During the last week don't run more than 6km each time and not faster than average speed.

This was the training schedule. Now a few tips I learnt and found very useful.
Buy the tickets and tell your friends as soon as possible. It's much harder to give up after that.
Buy 1 and half size bigger shoes, I bought half size bigger shoes and I lost 3 nails after the marathon. It was pretty annoying during the last 10km.
Drink as much as you can during the run, I nearly drunk at every resting spot. I used 4 Carbohydrate gels, 1 per hour. In theory more is useless as your body can't release more than that anyway.
At the NYC marathon there are the so-called Pace Runners. They are professional runners running the marathon at constant speed in pre-defined time schedule. I followed the guy with the 4h:00 sign and it made my race. Try not to run over your possibilities, you're going to pay for it, I took over a few guys who started faster than me, during the marathon.
One of the doubts I had was what to eat the day before and the morning before the race. The usual tip is to eat more carbohydrates but still avoiding revolutionizing your routines and stressing your body with something new. The day before I ate a lot of pasta, two big plates (lunch and dinner) and drank A LOT of water. In the morning, I ate a pasta 4 hours before the start, some cereals and fruits 2 hours before, a banana and two energy bars 1.30h before.

It's going to be a great experience, you'll learn a lot about yourself, your body, your limits, and you will not regret it.

Again: I'm not an expert, so take this as my diary, not as truth on stones. I read many articles, a book and some blogs, but that doesn't mean I'm right about all of this.

Some Acknowledgements: mom and dad for loaning me the money for the race, Marco and Anna for Baldini's book, Elia and Martin for training with me, my sister for the watch and the heart meter, Steven for the running shirt, Andreas and Stephanie for the after-party, Nasha for the support and hosting. And all those who told me I wouldn't make it, those were the most helpful.