How do candidates choose where to visit while campaigning?

Last election, I noticed that it seemed like the candidates came to my (very little) city a lot. This election, it seems like they have been here even more.
Just a few minutes ago a woman that works with my husband spoke at the Democratic National Convention. I feel, for being a relatively insignificant area that most people have never heard of, there is a lot of attention on us.

We do happen to be one of the places in the country that are doing the worst (I’ve posted about this before.) Is that why they zero in on us? I live in a swing state, so I assume that has some effect. How do they choose what small cities and towns they will visit?