There's a lot beauty to find in Guadlajara, no mistake. There are a few ordinary precautions to take -- wash your vegetables before cooking in a rinse of clean water and iodine, there is a common product that you add a few drops of into the water. Don't drink public water -- a lot of the buildings store their city water supply in open, roof-top cisterns where such things as drowned pigeons can be found. When I was there, ten or twelve years back, the watrer service was intermittent; I was lucky to have a place with a private well which drew naturally clean water from deep under the layer of jal for which the state of Jalisco is named, a chalk and lime substrate. But most homes don't have their own wells.
Out on the perimeter of the city there is a population of semi-feral dogs that wander around -- I once had to kick one of them five feet up in the air when he thought he would take a nip out of my daughter's toes on impulse. Just a minor random factor to be alert for. A lot of families in smaller homes keep a "roof dog" who serves as a burglar alarm and noise nuisance.
Learn from the locals how to deal with cops, especially if you are going to be driving. When I was there, we got held up by cops jus once, but it was a hefty mordida.
You can trust the dentists and doctors; we had several occasions to use them and found them very competent and helpful.
There is an "American University" there which is very good for learning Spansih as a second language. There is an extensive community of ex-pats, both UK and US, especially out by the lake. There are beautiful sights to be seen in the country all around, including ancient (pre-Columbian) pyramids that you sometimes come across by accident. The indigenous Indian cultures are an endless source of itneresting study.
Just don't expect things to be as predictable as they are at home -- be ready for anything and you won't be disappointed! :)