You can imagine how many people call me for good information on Mexico City. The town has so much buzz, and for good reason. It's a little intimidating if you've never been or don't have high school Spanish behind you but it's not impossible and you are likely to have an amazing time.
My first real trip was in the 1990s. I went alone before a friend good meet me later in the week. I had callouses on my feet from walking everywhere. I remember walking down a sunny street in the Centro, passed a Licuado store selling Mexican smoothies. I'll admit there was a skip in my step. I was independent and having a wonderful time. As I passed, a young girl yelled out from inside the store, "¡Buenas dias, guapo!" This was followed by giggling and I felt like I was on top of the world.
I feel stupid when people ask for suggestions. All the regular recommendations are probably essential for a first time visit. The museums, the parks, Frida and Diego's house, etc, are all great. For me, meals at Contramar and Pujol are necessary but I can think of 10 other places that deserve your attention. The reality is that these days when I am in Mexico, my friends normally pick me up at the airport and whisk me off on some journey. I haven't had a chance to linger in D.F. for years.
This is why I love Jim Johnston's Mexico City: An Opinionated Guide for the Curious Traveler. Jim has lived there for many years and seems to know exactly what I'll need. It's great armchair reading and even better to take with you. The 16 walking tours will make you feel like a local in no time.