Being a teaching assistant as a grad student is a weird position to be in. The university doesn't really fully consider you an employee or a student, the brunt of the teaching and grading workload can often fall on you, and you often have to make up for professors disinterested in actually teaching. If you find yourself in this position, there are a number of skills and strategies that I've picked up over 8 semesters (and counting) of being a graduate teaching assistant.
1. Time management: This is one skill that I've talked about in a previous blog post, and just as it is essential for being a graduate researcher, it is very useful for being a good teaching assistant. Unlike in many jobs, there isn't necessarily a set amount of hours you *have* to work each day as a teaching assistant (except for your regularly scheduled labs and tutorials), particularly when it comes to grading, so it's a good idea to be disciplined when it comes to your time. My first semester at Western, I was the teaching assistant for an essay-based course that had about 40 students per teaching assistant, and we had two weeks to grade the first essay. After waiting a few days to get started on grading, the remaining time proved to be not enough to comfortably grade all the essays in a reasonable amount of time, with at least one night where I was up until 2am grading. Definitely not something that is sustainable over the course of several years in grad school. So for grading assignments it's helpful to get started early enough and put in work consistently, so that you're not rushing at the end right before you have to get the assignments back to the professor.
2. Effective science communication: One course at Western I've been the teaching assistant for multiple times is Earth Rocks!--essentially, your basic introductory geology course. As a teaching assistant for this course, your main duties include teaching the lab sections, which focus on hands-on applications of geological concepts such as rock and mineral identification, structural geology, and geologic mapping. The first time I was the teaching assistant for this course, it had been almost a decade since I first took introductory geology as an undergrad. So, I had a bit of re-teaching myself to do, and most importantly teaching myself to learn concepts in ways that are accessible for and geared towards non-science undergraduate students, who form the bulk of students in the course. In the context of an introductory geology course intended for non-science majors, a lot of this boils down to having a good enough understanding of basic concepts (what minerals crystallize at what temperature and why that occurs, different properties of rocks, interpreting geologic cross-sections, etc) to be able to clearly explain to students, but it also involves a good deal of emotional regulation--that is, having the ability to patiently explain topics to students who don't get it the first time, or being encouraging whenever students confide in you their issues with science as a discipline, or their own struggles in science courses. Perhaps moreso than having an expert knowledge of any subject, science communication, whether for public outreach or in a formal classroom setting, involves meeting your audience/students where they are, and being focused on giving them the resources for them to get to a point where they can best learn the material.
3. Knowing your value as a worker: As I mentioned, the graduate student teaching assistant is in a weird position with regards to their status as a worker--sometimes they're viewed as a student, other times an employee--and the duties as a teaching assistant can vary wildly from class-to-class. As I mentioned, some essay-based courses provided two weeks to grade ~40 student essays, while others… gave half that time. In this kind of situations, one useful skill is the ability to advocate for yourself as a worker, and try and push back against unreasonable expectations that a professor may have for you. Track your hours.