San Miguel is beautiful, colorful, and friendly. It's been on my list for a while. I know so many people who have been there and love it. I will definitely be back but I learned a few things I'd like to share. Depending on how you like to travel, you'll either love it or take a hard pass.
First, let's talk about getting there and getting around. Flying into Leon, Guanajuato (BJX) is your best bet, although you could fly into Mexico City. The drive from Leon is about two hours and four hours from Mexico City. There are shuttles that you can take. I used BajioGo and it was easy to book online before I left.
I don't recommend renting a car. Once you get to San Miguel, you'll never use it. The city is very walkable and taxies are plentiful.
Second, where to stay. Location is everything. You can stay close to the Jardin (the central square) but it may be too loud for sleeping. Staying off the city square is okay because San Miguel is so small that getting to the where all the events are happening is very easy. I stayed south of the Jardin and it was fine.
As long as you can see the town's most famous symbol, the Parroquia of Miguel Archangel church, you'll never be lost.
The Colonia Guadalupe neighborhood is a great place to explore and see the murals, and the Colonia Balcones neighborhood for it's gorgeous contemporary colonial houses.
Third, a big concern in Mexico is always the food. Being that San Miguel is full of expats, the food is pretty safe. We went to a smaller town, Pozos, and that was a different story. If you go on an out-of-town adventure, take snacks.
Fourth, language. Know some Spanish! Even though there are a lot of Americans in San Miguel, the locals know very little English. Brush up on that high school Spanish and, if you don't know much, get one of those apps on your phone that does the translating for you.
For number five, we need to talk about the expats. There is nothing wrong with them. The locals and expats get along fine and they seem to be very respectful of the local culture. If you go during Day of the Dead, just be prepared to feel like you are in America. I went to the Catrina parade and discovered no locals participated, it was all Americans. There are still plenty of ways to experience the local culture. Just be prepared to see quite a few well-off expats. If you are bothered by that, then maybe go when there is not a festival of some kind.
San Miguel is a great town full of culture even if it's full of Americas and I recommend it. By the way, the photo above - she's American.