1. Absolutely how to write. A lot of your classes are going to have essays analyzing events in history, and is some cases having to complete them in class. Knowing how to plan (which is where some students falter a little) and write a complete, well rounded essay with a succinct beginning/thesis, middle, and conclusion within an hour or two is going to be one of your handiest skills. Purdue OWL was recommended by an AP English teacher and is a great reference.

2. How to cite and do research. Know where to find find what your looking for if Google can't help with the more niche subjects. I suggest online archives (the Smithsonian has a great one for visual works), libraries when some projects require physical citations. Archives are where I found some of the most perfect resources for my papers from the Lakota Ghost Dance to Byzantine iconography. Archive.org is a great site bc it has full books and movies among other things, and is free with an account. And I think most college students can attest that JSTOR is everyone's best friend, free with your school email. Dont be afraid to purchase your own books as well from Amazon or other bargain sites if your project needs a little more meat on the bones. You can also check the citations of the papers/books you're already using to find where the writer(s) got their information. By doing so I found that in one instance, every journal/book I was reading from had one common resource, and after I purchased the book it had literally EVERYTHING I NEEDED for my paper. Citation machine is good when it's 3am and you're too tired to write 10 or 15 citations, even if the website is a little janky. Has MLA and APA format and you can copy/paste.

Good luck dude, and happy studying. One more thing, as much as it might seem like a good idea. Do NOT pull any all nighters unless absolutely necessary. Too many mistakes can happen in that overtired, super caffeinated state and it sucks having to go to classes feeling like crap the next morning.