I'm defending my thesis in April. A couple things I've learned that are really helpful:

Start early - Seems redundant, but I can't stress this enough.

Once you find a topic you're interested in, read everything you can possibly find. I took notes on my computer and for every article I found I put the title author and date of publication as the name of the file. It makes it a lot easier to sort back through it later.

The internet is incredibly convenient but is no substitute for good skills in the library. I'm doing mine on slave trade suppression, so every week I'd go to the section in the stacks and grab a book I've never heard of. Also, if your searching in the catalog for a specific book, also check out the ones that are near it on the shelves. Serendipity is the name of the game. Some of my best sources I found on accident. Also mine indexes. Greater minds than you or me have done all this before and we're lucky enough that they kept a record of their sources and process. Don't buy books unless you absolutely have to. Use inter library loan websites, I'm sure your school has access to some. Some big ones I used were Illiad and WorldCat. Then use digital libraries like Haithitrust.org or EBSCO. Again you'll need special access but I'd be surprised if your school didn't have them. Also, never underestimate google or google scholar, but don't rely on them.

When it comes to primary sources, try to read an hour every night, it will get tedious sometimes, especially if you have to do long grinds, so spread it out. Also, the meanings of words change over time, so be vigilant for any subtle nuances you might miss by attributing the modern definition to the word.

As far as note taking, I found it better to take notes on ideas and themes on your first read through, that way you can read back through you notes and figure out what is relevant to your question. Then go back and read the sources you need again for more specific information. You'll probably end up using only half of what you read.

Once you have a good question or a good couple of questions, write these down on a note card and keep referring back to it while researching and writing, just to stay on track. Too often did I sit down to research then an hour or two later find myself reading something a couple centuries off.

Quality of analysis over quantity. My thesis will be around 20,000 words and when you're writing something that long, you'll find that at some point you have to stop yourself from writing more or finding more sources.

Learn a lot about stuff that you won't include in your thesis but is still relevant to your topic. For example, I'm focusing primarily on the British courts in Sierra Leone after the Slave Trade act of 1807, but I read books and primary sources about the abolitionist movement in Britain, which will maybe only be a page in my introduction. But it's important to know everything. This will come in handy especially for your defense.

Something that I always have to remind myself with my topic is not to hold people in the past to the standards of today. Even some of the greatest abolitionists were horrible racists, but that doesn't lessen what they did.

Depending on your topic, remember that it is really easy to criticize something or someone, but it's much harder to redeem someone or something and as long as what you're saying is true, I think a redeeming work is better than a condemning one.

Learn the historiographical evolution of your topic. This goes back to why I always wrote down the date of publications in my notes. It's important to know when people were saying what, and try to figure out how their time influenced what they wrote. Find your little niche, in the conversation and add your piece. Also avoid the historian Oedipus-complex, criticize your fore-bearers respectfully. They spent their whole lives working in their field, their opinion, no matter how outdated, should be respected.

Utilize your professors, at my school it's part of the job for tenure track professors take on advisory roles. The thesis is probably the best way for students to really connect with their professors. They know a lot and they want to help you. Though, when you meet with your adviser and you start bringing your writing, do the grammar and little things on your own before or go to your schools writing center. While I'm sure your professors won't mind helping you correct that stuff, you could learn so much more if you spent your time on your topic.

And start early, it's a marathon not a sprint. I had a buddy with a 4.0 get cum laude cause he always had such an easy time in school and thought the thesis would be the same. I also had a buddy with a 3.3 get Summa cause he busted his ass from the beginning. Hard work is the key.

Little warning: there will probably be times when you feel overwhelmed or unsure if you'll finish and you'll want to give up, but don't worry you'll get through it. Whiskey can help with that a lot too.

One last thing: Back in the fall when I was still in your position my professor said something to me that change my whole perspective. She said "If everybody could do this they would, and you're doing it for a reason and I hope it's because you enjoy it." I've been enjoying it ever since.

Hope that helps and good luck! Now back to work on my own thesis. Let me know if you have any more specific questions.