Guanajuato is really high up (in elevation) give yourself some time to adjust to the change.
While Guanajuato's climate is generally pretty warm, November through February can get a bit chilly, especially in the early morning, so pack accordingly.
On average, the warmest months are April and May. July through September is the rainy season, though overall, Guanajuato has a very dry climate.
Guanajuato is warm most of the year round, so pack clothing that's light weight. During the winter months, the weather can get a bit colder so long pants and light sweaters are advisable. During the rainy season (mid June-September) the weather is warm but prepare for intermitent showers.
Though Guanajuato is not a typical 'Spring Break' location, plane tickets from the US to Mexico can be more expensive during this time of year (typically mid-March through mid-April).
There are two airports in Guanajuato: Del Bajio International (BJX) and Captain Rogelio Castillo National Airport (CYW), which is a regional airport. You can also fly into Mexico City (MEX) and take a bus to Guanajuato via Primera Plus bus line.
Most of the cities in Guanajuato are very walkable so pack comfortable shoes. Many of the towns have cobblestone streets, and though quite charming, are not well suited for wearing healed shoes.
The bus system in Guanajuato is reliable, often airconditioned, and affordable. Taking the bus is a great way to explore the state and take day trips to other cities and towns.
Some of the best food you'll find comes from carts on the side of the road. However, be sure to wash raw produce before biting in.
It is customary to tip your waiter/waitress, bartender, musician, housekeeper, baggage handler, and tour guide. The customary tip is roughly 15%. If you see a line item on a receipt that say 'propina' this is the built in gratuity charge and no additional tip is necessary.
Many shops and businesses may be closed during mass or other religious or cultural holidays.
The last couple weeks of December and the two weeks leading up to Easter are often full of religious festivities. This may mean you'll encounter unexpected business closures so please be aware. You might also encounter street fairs and festivals.
When visiting churches please be aware of services and mass and please be respectful.
Most tourists to Guanajuato aren't English-speaking, so it won't hurt to brush up on your Spanish (if you're not feeling confident).
Public access internet is more available in larger cities in the Guanajuato region, and gets more scarce the more rural you get. There are many internet cafes in the larger destinations, frequently found near universities. Cafes, especially more established chains, frequently offer wifi as well. Public wi-fi access is available in some public places, though be wary about flaunting expensive electronics.
Unless you're already acclimated to the water, we'd advise not drinking from the tap. Also be weary of ice in your drinks—it's always best to ask.
In case of a health emergency, it is advisable to travel to one of Guanajuato's larger cities to seek medical care if at all possible. Guanajuato city has two large hospitals, Hospital General and Centro Medico la Presa. San Miguel de Allende also has a large private hospital, Hospital Tec100, located 3km west of the city.