I remember that transition well. When I went back to work after my first I felt sure my heart was going to break to leave my little one that first day but surprisingly it didn't. I was excited to be back at work and then even more excited to return home. It helped to have a lot of support from other moms who had gone through a similar transition. My sister who was also a working mom was a huge help to me. My co-worker another working mommy was also a great resource. My tips: 1- surround yourself with fellow working mommies. The support, feedback, tips, etc that you'll get from them is priceless. 2- Keep a notepad and make lists. I had significant "mommy brain" and I would forget everything if not written down! Also a list helped me to feel more organized and not overwhelmed. I had three lists: tasks for work, tasks for home and tasks for me (me time is important too!). It was good to check things off and have an accomplished feeling. 3- Keep a schedule, but don't expect it to be perfect. Especially if you plan on pumping when you return to work (Be encouraged..It is doable!) you'll need to schedule in breaks for pumping and work meetings or whatever else around that if you can. (I pumped between classes and on lunch break.) Spontaneity is hard when there's lots to do so I find scheduling in down time/me time, spouse time, baby bonding time, etc. Also helps to make sure you don't get burned out and you keep important relationships going too. 4- Be mentally prepared for "crossover". We all try to leave work at work and home at home but we are human and we can't just drop everything at the door and compartmentalize. So be prepared for the crossover, sometimes you will be thinking about baby at work, and sometimes you'll think of work with the baby. Instead of fighting the feeling give yourself a break sometimes its okay to mix the two. You can chat with a coworker about your baby's newest tricks. And you can answer a work email while cuddling baby on your lap. Just keep in mind not to overdue it. Stay focused 90% of the time and those 10% crossover times wont matter.
Hope this helps. Have a happy transition back to work!