Some people saw that their entire graduate school experience was stressful, but I would say that there are only a few points along the path that are truly stressful. The first term is the earliest of these points. The first term involves getting used to new professors, taking classes that are (in some ways) more challenging than those in undergraduate, trying to find a research group, and getting used to the workload of being a teaching assistant (TA). Each of these activities can be stressful by itself, but you are also trying to find a balance between everything and you may or may not have someone helping you to find that balance.
First off is the classes. Keep in mind that I am in the chemistry field so class structure and amount of work will likely be different if you are in another field. Many people would say that graduate level courses are more difficult than undergraduate for varying reasons. They are usually higher in class number, they move at a faster pace than undergraduate courses, and they usually only have a couple of graded assignments that determine your grade for the course. I took a couple of graduate courses as an undergraduate, which I highly recommend to anyone considering graduate school, and that showed me that these courses are different, but not necessarily harder. Yes, my grades for the class were usually only determined by a midterm and a final, no homework assignments in between, but that also meant I wasn't swamped with homework while trying to do research and teach. The professors also give themselves a lot of leeway in how they grade, which can help or hurt you. I have had classes where I got in the 70%'s on the midterm and the final, but the professor was able to see how much I knew through my conversations with him and by the problem solving activities we did in class so I was given an A- for the overall grade of the course. I have also had classes where my classmates had slightly better grades than I did on assignments, but the professor liked me personally so I received a slightly higher letter grade at the end. Some classes were also on a curve, and in grad school you need B's instead of C's to be able to continue on, so the courses were curved to a B instead of a C. This meant that you only needed to be in the middle of the pack and you would be safe. The best thing to do, is it learn as quickly as possible how the professor teaches and how to interact with them. You need to be able to adapt to multiple teaching styles and personalities to do well in classes. The final note is to make sure you get a good night's sleep before a test. The tests that I have had are not for the students to memorize and regurgitate information, but to use the basics they learned in class to solve problems. Once you know the basics, there is no point in becoming overly stressed about the test, the best option is to go into with a clear and concise state of mind.
The second stressful activity can be finding a research group. In my case, I already knew what group I was going to join before I had moved to the area and started my first term. This meant I didn't have to really worry about finding a group, but I saw what others went through and so I can give a little advice on this. First of all is whether or not your department does rotations. If a department does rotations then you will pick two or three research groups to try out and you are not expected to make a commitment until the end of your first term. This can be good because it gives you options, but it can be stressful because you need to show that you can be productive and you need the professor and other graduate students to want you in their group. My department does not do rotations, so it is up to the students to try different labs if they want to or to find a lab and instantly join. This can give the student more work because labs fill up at different rates so there may be a lab you are considering, but they could stop taking new students before you've made your decision. There can also be scenarios where your department limits the number of students a professor can take based on if they have tenure or not. My department limits the amount of new students if there is a drastic shift in how many students want to join a single group. This scenario rarely happens, but a new untenured professor did do a great job at recruiting so 80% of the students wanted into their lab which meant fewer students for the tenured profs. Just keep in mind that you need to make an informed decision as early as possible, otherwise you may wind up only having the option of joining a group you don't like or dropping out of the program.
The final task that eats away at your time is teaching. This can vary greatly depending on the workload of the class you are teaching. For my department, some students do the general chemistry course which means two recitations and two labs with approximately 25 to 30 students in each one, but the introductory chemistry course doesn't have a lab. For the introductory course, the TA's do six recitations of 50 students per recitation so they end up grading 300 quizzes and 300 assignments each week as where the general chemistry TA's do 60 quizzes and 60 lab writeups. There is clearly a divide in the amount of grading each TA does, but the general chemistry TA's spend eight hours a week in recitation and lab while the introductory TA's spend six hours in recitation a week, all the while the introductory TA's have more grading to do each week as well. Unfortunately, we did not get to choose which labs to TA our first term so it was a luck of the draw on if you got the introductory course or the general course. The best thing you can do in either case is to find ways to grade efficiently so that you are not taking any longer than you need to. The professors that you TA for will tell you to take as much time as possible, but this would never work because you need time to do other things. The best thing to do is to talk to your other classmates and see how they grade. Most people can come up with a tip or two on improving their own grading so if you could gather the tips and tricks that several others have discovered, then you could find which ones suit you best to reduce the amount of time spent grading.
Of course, on top of the trinity of graduate life (research, teaching, classes) you want to be able to do stuff that you enjoy. Let me change that, you need to do stuff that you enjoy! If you don't do activities outside of graduate school that help you relax, you will get burned out and be miserable. Find what you can do in your work schedule to take breaks. Go outdoors on the weekend, go socialize with other graduate students (keep the research talk to a minimum), stay indoors and be lazy one day a week.
