This may be a terse response, but as an undergraduate, the best and most important things you can do are to work the hardest to get into the best graduate programs you can in the specialty you are looking to get into. Even if your goal is to become a high school history teacher, you will at least need a master's degree in education, and honestly, I am guessing that is not your end goal.

There is a considerable amount of competition for the jobs that are strictly History, or Archaeology sorts of roles. The jobs exist, but will necessarily go to the best of the best academically, the best connected, and frequently those who have both going for them.

To be frank, in any highly competitive field, connections are hugely important. That is why you want to know where you are going and work to meet with the people who are already where you want to be.

I'd say that aside from your ability to get published and otherwise do good research on your specialty, this is probably the most important thing you can work on. That's why you want to get to know your advisor, who has already succeeded to some degree in the field you are trying to get into, for instance.

In undergrad, you will want to have very good relations with your advisor, and you will probably want to select an advisor who at least has some relation to your intended specialty or your intended grad school. It would probably be good to try to get to know the other profs as well, but honestly, you may have limited ability to get more than your advisor's attention if you go to a big school for undergrad. Make sure you are attending their classes as many semesters as possible and are a (well performing) fixture every year.

You will also want to take any opportunity you can to be a research assistant and contribute to anything related to published research. You won't likely be published yourself, of course, but you will want to understand how to compete and the function in the world of obtaining research grants and publishing. This may also allow you to interact with other people in the field.

Again, remember, the work you will likely do as a research assistant will be grunt work, your job will be to do the best you can at it and become a name and face that the researchers know, as well as learning the ropes.

You will want to identify the graduate programs that are known as the best in your specialty and be ready to pursue your Ph.D. for the long haul. Your list of grad programs should be well researched because you will want to do your best from day one to get into the top schools on your list.

Also, be aware that a lot of academic work is not in English, and depending on your specialty, your primary sources may be in one or more languages you don't already know. You may want to identify those and become more or less fluent in them, at least written. For my undergrad I studied Spanish, Russian, Latin and Arabic.

Oh, and in case I didn't mention this before. Connections. If you have family friends who are in the field or in academics, talk to them. I mean it. You probably don't have to be as desperate as those people trying to sell scripts to movie producers in LA, but it would certainly not hurt to have your work ready and be ready to do what it takes to meet the right people and discuss your work, research efforts and interests with them.

Finally, if you are concerned about serving coffee or otherwise not using your degree the way you wanted to, know when it is time to pull the ripcord. If you're only middling in your major in your undergrad and especially in any post-grad work, you're looking at a degree you won't have the opportunity to use unless you really do have some connections that can finagle you a job.