When you move to a new place, it can take a long time to set yourself up. Finding housing, setting up local back accounts, phone lines, internet, registering to vote, getting a new driver license, registering your car, changing all of your addresses on various accounts, etc. can be time-consuming and annoying. Also, getting set up at the university (i.e. getting IDs, setting up payroll and benefits, getting keys to various offices, obtaining your library privileges, setting up your office at work, etc.) can be a hassle, even if there are no problems! Thus, I suggest avoiding these tasks during your graduate school orientation! Try to arrive at least couple of weeks before orientation. It will make it a lot easier on you.
Once you are set up at home and at school, it can take a long time to acculturate. Especially during the first year, you will expend a lot of energy taking in new information about your environment, even though you aren’t aware of it. This will make you tired. Research shows that the more tired you are, the less productive you are. So if you can, budget a certain amount of free time each week, and commit to it even when you feel overwhelmed and busy. Depending on deadlines and other commitments, at different points I’ve found it useful to stop working at 6pm on weeknights, to not work on weekends, or to take two weekends per month where I don’t work. The more you can keep these commitments, the more productive you’ll be when you are working.
You’re going to do a ton of reading your first year. It will be overwhelming. If possible, find out what some of the books will be during your first semester, and read a couple of them the summer before you arrive.
Join your disciplinary professional association. If you’re a political science study, join the American Political Science Association (APSA). You can do so at www.apsanet.org. Your membership fee will include subscriptions to three useful journals: American Political Science Review (the top field journal in political science), Perspectives on Politics (a research-oriented journal that comments on current events), and PS: Political Science and Politics (a journal on the profession, regarding research, teaching, and trends in the profession itself). It will also give you free access to e-Jobs, where you’ll find out who is hiring (academic and non-academic) and who is offering pre and post-docs. You will also be able to register for the APSA Annual Meeting at a reduced rate. The International Studies Association (ISA, isanet.org) is useful for international relations and comparative politics, as well as international studies more broadly, and it holds a large Annual Meeting each year as well.
Go to APSA (and ISA, if relevant) as soon as you can; see if your department has small travel grants to support your trip. (APSA and ISA both have limited travel funds for graduate students presenting at conferences.) And plan to go to APSA for sure the year before you go on the job market, and the year you are on the job market. There are also regional conferences (i.e. NEPSA, MPSA, WPSA, SPSA, etc) where you can network and get practice delivering papers, but they are often closer to home and are (sometimes) cheaper, depending on proximity.
You’re going to want to look at the IR Rumor Mill, the polisci wikis, gossip boards, etc. I suggest never looking at them. They will only distort your view of the field. They are increasingly frequented by people who seem to have little grasp on the profession; moreover, they often spread very malicious and unfounded rumors that will affect how you see your colleagues even if you try to remain impartial. My best advice is to stay off!
If you are a TA, don’t date your students. Sounds obvious, but it’s important enough to include on first-year advice.
Finally, savor this time! There may never again be a period in your life when your job is simply to read a ton of material, critique it, engage in fascinating intellectual conversations, and develop your expertise in your chosen area. When you look back at graduate school after you’ve landed your dream job, you’ll realize what a sweet time it was. So enjoy it, and stay in touch!