This subreddit has made it very clear that you should not get a PhD in history, so it is fairly safe to assume that a full-time Masters degree in History is also a bad idea. Since most online Master's in History are expensive and of dubious quality; how can the motivated student of history gain sufficient grounding in historical research methods? Presumably this is the student that wants to move beyond just consuming history (i.e., reading books, reciting the arguments of others) and contributing to scholarship in some way.
As a lowly undergrad, I think there’s still plenty to be done as far as engaging in history without the graduate-level training.
As far as general research methods go, methodology may vary depending on what you’re doing, but this is what I was taught in terms of the basic method. You will start with a topic you want to dig into, or a question you want to answer. You don’t want this to be too vague (saying “I want to learn about the Civil War” will have you lost in the weeds forever) but you want to keep it open enough where you can feasibly do some investigating and answer (so, for instance, my last research project started with “I want to explore newspaper coverage of Bleeding Kansas somehow”). If you have that idea, you’re going to want to get sources, ideally some mixture of primary and secondary sources. I’ll write on accessing those in a bit. Usually, the secondary sources are going to serve as a background and will let you have some discussion of what scholarship has been done, while primary sources allow you to add your own interpretation to the mix. Writing it is kind of similar to other writing, where you want to organize your ideas in a way that makes sense, and you want to make sure that you’re clear in communicating them. Also important is making sure your sources are reliable, so make sure you know where a source came from, what sort of press published it, how old it is (you don’t want 100-year-old research on Reconstruction, for example) and what the purpose was in writing it.
If you want a very basic read on how to do that, we read this as an intro for one of my classes. I also loved this book -- it's not a "how to" (it's actually a medieval micro-history!) but the author walks you through his methodology in every step of his history, so it is a nice representation of things historians think about, so I think it's useful for a beginner.
So, the sources themselves:
It’s important to read secondary sources, both to give you a solid background and so you can see how scholars are interpreting things. With books, you can get some of them through inter-library loan, and if you’re near a university, their libraries are more likely to be stocked with these. If you have no idea what to read, the sub has some recommended books, and you could probably find more by scoping out course syllabi and things like that. For articles, you can check online databases like JST0R, which some libraries will offer to members. Sometimes writers will send you their articles if you ask nicely. The other nice thing about secondary sources is that you can find more sources in footnotes, so if there’s something you want to dig into more, you can.
It’s also great to get into primary sources. Some of these are published, but if you want something else you can always check online databases, archives, and museums. I recommend doing an archive at least once – usually they will have finding aids that tell you what you can find in a collection, or an archivist will be able to tell you if they have any material on a subject you’re interested in. Sometimes some online digging is nice – when I looked at newspapers, I thought the Library of Congress Database was super useful. The thing with these sources is that you’re either going to want some idea of what you’re looking for if you’re searching online or you’re going to want to pick something you find and build from there, because they can be a little messier to dig through. They’re so rewarding, though, and it can be fun to blindly dig, because you never know what you’ll find!
Also, if you have a local university with professors who teach what you’re into, don’t be afraid to ask them questions. Obviously don’t flood their inbox with emails, but I’ve found that usually they will be more than willing to recommend sources on a subject if it’s something they specialize in.
As for contributing to scholarship:
If you truly want to add to a broader historical discussion, my (biased) suggestion is going to be local history. Local history can be a little tricky in that finding the sources may take more digging, BUT there are plenty of things to be found, and if you find something big enough or put something together, you can absolutely impact your community that way. Many of the people who are involved in putting up historical markers and giving talks in my region are not historians -- they are long-time hobbyists who channel their passion into spreading their knowledge. You can also tie that into a broader narrative, too, if the era is interesting to you.
If that's not your cup of tea, you can always do something like blogging, making a social media page, or doing write-ups here. You're then free to pursue whatever random thing catches your interest, and you still have that external motivator to research and discuss your findings. I think it is unlikely that you will get printed in an academic journal or through a university press, but other than that, the sky's the limit; David McCullough is certainly not a historian but he's written best-selling non-fiction books about historical topics. It's all about finding where your interests lie, digging in, then finding the niche where you can spread that to other folks.
That Monday Methods post predates my time here but I kind of disagree with the advice...I mean, if the advice is "do not get a PhD expecting to get a tenured teaching position at a university", then yes, the advice is 100% correct, don't do that. It's not going to happen.
But you can get a PhD in history just for the sake of doing it, and still do something else with your life afterwards. You'll probably develop/hone a lot of skills that will be useful in the job market, even if you don't realize it; for example you'll probably have greater research, reading, writing, and speaking skills than other employees, along with time management/stress management skills. I know this sounds like the sort of thing you'd pad a resume with, and it looks a bit silly written down like this, but these are all things that employers are looking for.
Of all the people I went to grad school with, a few did get teaching jobs, but even then things aren't guaranteed - sometimes even if you're on the tenure track, they can just cancel the process and you're SOL. Some people I know always wanted to be a university professor and nothing else, and they never got any teaching job at all, and they didn't know what else to do so now they do nothing. Others went back to school to do even more degrees (library science is a popular one...law school of course, journalism...also museum curation!). I know some, priests, people who work for book publishers (academic and non-academic), therapists/counsellors, some people have even gone into local politics.
For me, I had a full-time night-shift job while I was in grad school during the day. I would definitely NOT recommend that (do you like sleep? You should!), but it was great experience since I was already working outside the academic world. Now I work as a translator, which combines all the skills I learned in grad school with the non-academic experience I had. I feel strange telling people about this sometimes...it seems like it boils down to "live my experiences exactly as I did" which is obviously not helpful, but my point really is, you can do lots of other things even if you have a PhD in history.
You can even stay involved in the academic world. I know it seems like university professors have all the time in the world to do research and write, but they have a full time job and they do their fun research in what is essentially their spare time. And so do I! It's true that it's harder to access libraries and other resources, but I think things are starting to change...if the vast majority of PhDs don't end up being professors, then wouldn't the way the whole academic world works have to change to reflect that?
I don't know about other sub-disciplines of history, but at least in Medieval Studies, there are some movements underway to include and support unaffiliated scholars (or independent scholars, or another popular recent phrasing, "alt-academics"). It's not perfect and there's still a long way to go, but it's a start.
So, in short, if you want to get a PhD, and you're able to do it (mentally, physically, financially), why shouldn't you? You're just not going to be a professor, so don't even bother dreaming about it. Plan to do something else from the beginning.
I have previously written about how to find sources and put them in context when writing a history book, which has links to many threads that will be of interest to you. I am /u/voyeur324.