My two cents..
I attended the race with my wife in 2013).
Except for perhaps my first in person race (2000 at Indianapolis) it was my favorite of the 12 races I have attended in US, Canada and Europe.
We stayed in Milan at a hotel virtually across the street Milano Centrale so it was an easy stroll to catch the train. You don't need tickets for the tree train to Monza so don't waste time looking for them (like we did ). Just go up to the platforms and look for the huge crowd of folks dressed just like you in the kit of their favorite F1 team and join the scrum to board the trains as they arrive approx 30 mins apart.
The Sunday trains go directly to the track and drop you outside of the Lesmos.
Definitely walk around see as much of the track as you can. There are lots of places you can get pretty close to the cars as they go by. I loved watching them come screaming up to Seconda Variante, hard on the brakes and then back on the power as they headed off to the Lesmos. So cool.
Enjoy the crazy joy that is the post race ceremony on the main straight, the sea of Ferrari red and huge flags. So great.
Try not to rush off too quickly after the race if you can take the time. Definitely walk the track and go down to see the old banking by the Parabolica. Amazing to imagine the old cars on the unbelievably steep banking.
TIPO61 had great advice:
Breathe REAL DEEP!
Take in as much of it as you can.
You'll remember it for the rest of your life.
It's a Spectacular place and a helluva race.
Enjoy, Enjoy, Enjoy.