You can find some schedule information on the Internet, and no doubt this will increase as time goes on. But, for now, going by bus means a leap of faith. You must have faith that buses go just about everywhere and frequently. In guide books aimed at independent travelers, you'll probably find addresses of bus terminals, but these change. Ask waiters, taxi drivers, fellow travelers.
Safety is also a concern.
Mexican buses get a bad rap stateside, with accounts of attacks, robberies and accidents. However, these are rare when compared to the number of buses and people using them. Incidents happen anywhere you travel, and it makes sense to be careful. Below are some tips to make your ride smoother and less frustrating. Maintain a positive attitude.