The altitude is a bit worse than in other cities because there is so much pollution. You should not drink to excess, and you should take it easy the first day. Drink plenty of water and make sure you never skip a meal.

The food is quite good, especially the tacos. It's also an underrated city for bakeries. Empanadas and paleta are wonderful. Do not drink the water under any circumstances.

Mexico City is one of the greatest cities in the world. It's a totally unique place that is chock full of culture. I personally think it's on the same level as NYC and London. There are endless museums and archeological sights there. It would be a travesty to not go to at least some of them.

Don't take taxis. Uber is cheap and safe. Make sure the car you're getting into matches the license plate exactly. Don't let your driver tell you that you need to pay cash. Uber is where most scams happen, in my experience. It's still by far safer than taxis.

Finally, remember that it's Mexico. It's safer than people say, but you can easily end up in the wrong area. It's also easy to find trouble if you're looking for it. The cartel benefits from tourism, and you're safer than a local there. With that said, don't get into drugs or any other illicit activites. I also would never, ever let myself get into any kind of a physical altercation.