Once you can answer all three of these questions confidently, use your University's library to find books which are relevant to your answers to said questions. Read them thoroughly. Once you have done so, look at their sources, and take note of the authors and books which appear therein. See any common names/books showing up? Pick up that book and read it too. Make sure you are well read on the secondary sources related to your topic of choice, pay attention to common methodologies, conclusions, and perspectives. Where do you currently see gaps in the research of this field?
If you can, find the nearest branch of Phi Alpha Theta. They publish a quarterly undergraduate research journal called, "The Historian." Definitely speak with any professors at your University who would have relevant experience in your selected area. They will be able to give you quite a lot of information that you may have missed.
I'm going to try not to repeat as best as possible, although a majority of great info comes from /u/NorthernIron, but here's advice from an MA student who has been published.
(1) Once you have an idea of what your field is, even if it's two fields, look at the faculty at your university. Anyone there who does your stuff? Several? Great!
a. Find out office hours and shoot them a polite email, saying you are wanting advice from someone in the field. Make sure you do some research on classes they are offering, and if something you love, hop into it!
b. When you meet with them, let them know where you are at and then ask for advice and guidance. Instructors tend to have dead office hours, and it's their field. Of course, they love talking about it with someone interested!
(2) Look at your university for a few things.
a. Does it offer an option of undergraduate honor's thesis through the history department or honor's program? Hunt around and see if you like the idea of writing a longer paper. It depends on your goals. I wanted grad school, so I wrote a long paper involving my topic and primary resources, but most schools let you tailor this thesis for what you are wanting. But lemme tell you, it'll drag you through a ringer of fire if you have a committee who knows your goals, but you'll feel so much more confidant about a long paper once you've done it.
b. Are there any publications for undergraduate work at your school? Check out the website! Also, talk to that professor you've chatted with earlier. I got two minor publications offered to me purely because he was putting together as editor and someone dropped out. Student publications aren't always accepted in such places, but it was a really lucky scenario that I was surprised by. I got put an online publication by my university. None of this is very big publication, but it was really great experience and practice. Obviously you can do a lot more than I've done, if you put your mind to doing it.
(3) Now, lastly for publication, you need to do research! The internet is a wonderful place to hunt for undergraduate journals but only once you find your field is the hunt going to be manageable. /: And then if they have their journals online, hunt through recent editions. What are they commonly picking? Not picking? What's the style of their publications? More traditional? Not? Etc.
As for writing skills?
Practice makes perfect. Doing your work ahead of time so it can marinate! Giving it to a friend to read and then reading it aloud with that distance? You end up with a much better work.
Plus, if you are looking at the rough draft, saying "Hey, my argument is really weak here. It needs more to back it up," you have time to fix it. You have time to look for that and really hunt for the right word, the right title, and really hone the paper to what you want.
And when you get it back, you can look over the professor's notes and even go to the office hours of the professor saying that you want advice on how to be better. Sometimes you have a TA reading your work, so talk to the TA about your paper too. Again, sometimes you just need a fresh pair of eyes to point out where you struggle.
Finally, two books pop up a lot from my instructors when they are advising better skills: (1) How to Read a Book and (2) Historians' Fallacies.
I've only read parts and pieces so I speak from a shaky platform for that last bit, but hopefully this whole thing gives you a good idea of where to go from here.