You will need to get a Ph.D. in History following college. I believe the average time it takes nowadays is around eight years. I hope you're going to a top-rated college, because that will make it easier to get into a top-rated grad program, because you will need this kind of clout when you go on the job market. I have heard the recommendation that if you can't get into one of the top 20 grad programs, forget the whole deal, because you won't get a job.

And that's the ultimate kicker: there are no jobs. You will be most likely to get an adjunct teaching position. This means you get paid per class, there are no benefits, and it's not tenure-track. You will have no office, and will keep all your paperwork and supplies in the trunk of your car, to make it easier to travel to the various schools at which you will need to teach to make ends meet. You will literally be living near the poverty level, because the glut of historians makes it possible for schools to pay low wages.

You might be able to get an adjunct position with only a Masters in history, depending on location and other factors. For the most part, a Masters in history is not an ultimate degree, unless it's something specialized like public history.

Private (and some public) high schools might be interested in hiring Ph.D.s. But in ordinary circumstances, if you want to teach high school, you get a major in Education and get certified in your state (assuming you're an American). You get all this taken care of in college. It's an entirely different track than teaching at the college level.

I recommend you keep history as a hobby, and get a degree in something that will allow you to merge neatly into the post-industrial workforce.

What Carol_White said is very true, and professional historians actively try to throw cold water on potential historians because it is really really hard to get a job as a historian, let alone to get through graduate school. Graduate school is terrible. You put your life on hold for 5-8 years, you work ridiculous hours for next to nothing, you are the bottom of the totem-pole, you go through intense stress over and over.

With that being said I will add a few things to pursue if you still want to try.

• Top Schools: Carol_White mentioned this in passing and it is true. It is only really worth going to a top 20 (hell probably more like top 10) school for a PhD. These are the schools that pay you to pursue your degree (note they do not pay you well, you will still more than likely accrue debt). These are the schools that, if they are on your CV, result in you not going in the discard pile when a Hiring Committee is trying to wade through 300+ applications for one job. So, do your research. Find out what these schools are in the field you are interested in. Obviously some schools (read Ivy League, UC Berkeley, a few others) are top no matter the field, but other places happen to have a phenomenal Asian or American or Medieval program based on faculty and the like. Your adviser/professors can probably help with this, and college rankings do give you some idea. Never go to a school that is not paying you. Never, ever. Grad school is an apprenticeship program, it is not just "more school."

• Languages: This is probably the most important thing you can do as an undergraduate to both increase your chances of getting into a good program and to help you prepare for life as a historian in any field. All historians are expected to know at least one foreign language. Most historians know at least 2-3. Medievalists know Latin as well as French and German (and whatever relevant language they need to pursue their own research, such as Italian, Dutch etc.). Asian Historians likewise will need to know a minimum of 2-3 languages (both Asian and European). This is so you can do research both in the primary sources and so you can read the vast body of work by other historians. Find out what languages your chosen field needs (look at grad school websites for this info) and get at least one down before you apply. If you can get 2, awesome. Generally you need to be able to read, not speak, though speaking is a bonus of course (especially if you are going to be doing research abroad, then its a necessity).

• Reading: Read a lot of history. By this I do not mean primary sources. I mean reputable, high end history written by historians. Read articles, read book reviews, read books. Find out what the major professional journals in your field are (the American Historical Review is #1 in America, but is non field specific) and start there. Read and look not for info but for style, argument, skill, etc. The actual facts of history are "easy," they come with time, effort, and experience. Thinking like a historian (being able to read evidence, make arguments, use other peoples work, etc.) is really what Grad School teaches you. Get a leg up on this.

• Writing: Work on your writing. You will be doing a lot of it. You will be writing papers, articles, chapters, books. This can be linked to reading. Read and see what good writing looks like. Take as many classes that require papers as possible. Yes it will be more work than the easy throw away courses but it will help prepare you for what is essentially your main job as a historian.

• Classes: Choose your courses wisely. Obviously classes in your discipline of choice are important, but if you see something interesting in a related field, go for it. Breadth in undergrad is good as long as you don't over-do it. Again, you will be expected to have the basics of your field when you apply for grad school (so at least an upper division level) but taking sociology classes, anthropology classes, lit classes (especially related to your area of interest) are also immensely helpful. Undergrad is, at its heart, about teaching you to think critically and become a well-rounded person. Take advantage of this.

• Cultivate relationships: You will need letters of recommendation. Letters by someone who actually knows you are better than letters from a professor you took a lecture with once and never talked with. Go to office hours. Talk in class (but not too much). Be polite and engaging, not cloying or overly-enthusiastic. If you go to a school that has an adviser system (i.e. not just one big department or school adviser), get to know your adviser actively. If not, figure out who you think will be the best fit for you and cultivate a relationship with them. Not only will you potentially make a friend and ally for life (most PhDs and Grad Students I know are still in contact with their undergrad advisers/mentors) you will be learning a skill (engaging with faculty) that will be of immense importance as a graduate student when your life and career will depend heavily on managing your relationship with your adviser/chair. On this same note, god help you if you are an introvert. So much of being a professional is going to conferences, meeting strangers, maintaining connections, asking questions in big rooms full of people etc. If this sounds terrible, then History as a profession is not for you.

So yeah, there are some tips. I stress again, it is a very hard life to undertake and only very rarely rewarding. You will most likely not get a job. If you do, odds are it wont be the job you want. But if you still are interested, best of luck.