What are some steps an undergrad can take to get on a Ph.D. track? I hope this question isn't too broad. 
I'm graduating next semester and I have been accepted into grad school, but I'm having difficulty finding a full map of what one should do to successfully go from where I am now, to a Ph.D., to (eventually) a tenure track--hopefully as a full-time student through the process. Obviously, this is over the course of 10+ years, but I want to do everything I possibly can, as early as I can. 

Some things my advisors have told me for the near future:


Write a thesis as part of your Master's program
Find a professor to research with (goes with the first bullet)
Go to at least two different schools throughout the whole process 


Undergraduate advisors didn't have very much advise past that. I'm looking for a broad roadmap of what my future would require/look like if I were to go down this path.
Many students who want to study for the PhD in the US apply directly at graduation from their undergraduate education. A MS isn't needed for most fields, but might include one along the way for little or no additional effort. But expect that such a doctoral program will include additional coursework in your field prior to starting research, and, perhaps, prior to choosing a research advisor. 

The advice you were given is good, but the MS isn't actually needed (most fields). What you need is a solid record of accomplishment and good letters of recommendation that suggest you will be a success in graduate study. 

The advice about going to more than one school is so that you have more opportunities to view a variety of approaches and a wider range of ideas than you are likely to get if you stay at the same institution throughout. 

In some doctoral programs you can get a MS just by asking for it and paying a fee (some paperwork). In some you write a thesis of lesser scope than a doctoral dissertation, but possibly giving some practice with research and writing. 

The path might be something like 6-8 years, possibly as long as 10. 

You need a way to support yourself. The common way is to serve as a TA in your doctoral department. Research Assistants are open as well, but to fewer people in some fields. 

But in the US, the best advice for right now is to apply to a few programs that interest you, including some that are more likely to take you than some others.