Speak to HR about a private and secure room for you to pump in. The Affordable Care Act in the US requires most places of employment to provide one. I would recommend emailing or calling HR prior to your return to work, in case they need to change your security access settings or add you to a schedule with other moms.
Buy or borrow a second pump for the office. I know this can be an added expense, but trust me it will make your life so much easier. You really don’t want to be carrying a pump back and forth to the office every day, so it is much more convenient to have two. Try asking a local moms group on Facebook to see if anyone has a pump in good condition they are looking to get rid of.
Keep multiple sets of parts, depending on how often you are pumping at work. By doing this, you can take all your parts home at the end of the day and wash them there instead of in the office. Much more convenient and hygienic.
Think about how you are going to store and transport your breast milk. I would advise using the work fridge during the day if you are comfortable with it and bringing it home in a cooler. If you would rather not do that, then you can buy a cooler and freezer packs and simply keep it with you at your desk, also a more discrete option if pumping at the office makes you feel slightly uncomfortable.
Block out time in your calendar to pump. There is no shame in prioritizing this, and there’s nothing worse than being stuck in a meeting and feeling like you are bursting. Simply make an appointment with yourself in your work calendar and mark yourself as unavailable.