Having to go back to work and the associated stress can really do a number on a mom's sense of well being. Trying to balance the demands of pumping while at work can be a huge undertaking and lead to significant stress. Often moms become panicked about their supply once they begin pumping and can physically see milk quantities instead of just breastfeeding and watching baby grow.
Generally speaking, your best bet is to pump at the times baby would normally feed. Part of the Patient Protection and Affordable Care Act (Obamacare) worked hard to address the needs of nursing moms who go back to work. The law provides for breastfeeding/pumping equipment to be provided through insurance (check with your insurer for details) and requires employers who fall under the act to provide adequate facilities and time so that moms can express breast milk for her nursing child (up to 1 year after birth). You can read more details on federal breastfeeding laws here.
Moms are often shocked by the amount they express when they start pumping. There are several factors at play that feed into their concern. First, effective pumping will generally empty about 65% of the available milk, babies on the other hand will empty about 85% (on average). Second, when baby is bottle fed in the traditional methods, they will drink about 25% more than they'd comfortably drink while breastfeeding, this can lead parents and caregivers to think baby needs more milk than is actually required per feeding. Third, when mom is home, baby can be fussy and demand more time at the breast. This is called cluster feeding and can be attributed to both a desire for food and comfort. In my experience, when mom has been gone for a while, baby likes to nurse more frequently as a way to reconnect. Babies may also choose to reverse cycle when away from mother during the day. This means they will choose evening and overnight as their high demand eating time, instead of during the day. They do this because they prefer to eat from mom and be with mom, it can be a bit exhausting sometimes, but it is all out of love.
Generally speaking, a mom who is away from baby can expect to express a total of 2-4 oz per pump session. Because pumping will always remove less than baby can, this can lead to a tight supply of expressed milk. There are a couple of tricks you can use to make sure there is adequate milk available for baby when you have to be away. First, you can add a pump after the first morning feeding. Because your prolactin level speak overnight, you generally have a lot more milk in the morning vs the evening. By pumping off the excess after baby eats in the morning, you can add to your baby's stash during the day. Second, if you can swing it, you can pump once more than baby would eat while you are away. I have been told (and noted from personal experience) that your body will produce milk when it expects to be used, so a consistent pumping schedule will also help you achieve the results you are looking for. Kellymom has a great article on how much milk is needed when you are away from baby. You can read it here. Kellymom is an amazing resource for all breastfeeding questions in general, if you haven't bookmarked it by now, you really shoud!
Another way to help ensure your baby has all the milk they need is to have caregivers practice paced bottle feeding. Paced bottle feeding has many benefits, not the least of which is helping make sure baby doesn't eat and preventing flow preference issues that can make breastfeeding more difficult. This is my favorite video for paced bottle feeding techniques.
Pumping is all about technique and mental cues. The letdown reflex can be trained, which is something you can use to your advantage. When I pump, I always have ice water with me and when I hear the pump's letdown sequence, I always drink seven swallows of water. Over time, following that same routine helped my body cue that the sound plus the water meant it was time to release milk. You can use any cue you'd like to achieve the same result. Here is a great article from Kellymom on working with letdown and cues you can use both for nursing and pumping.
Additionally, when you pump, you should use hands on pumping techniques to maximize milk expression. This video from Stanford's Lucille Packard hospital is fantastic for learning hands on pumping techniques. For me, I find hands on pumping practically impossible without a hands free pumping bra. After years of pumping, I've found that the bra I like best is the Simple Wishes bra (now with even more awesome options such as all in one versions and more color choices!). I also hand express directly into the shield when I am finished pumping. I can get as much as another ounce out by hand expressing using the marmet technique.
To make my work pumping life easier, I have several sets of pump parts. I keep one at the office for emergencies (which has come in handy for myself and several of my coworkers). I also bring all the sets of pump parts I need. If standard breast shields aren't working for you, you may want to look into the pumpin pal shields. If you need a hand pump, I'm hearing neat things about the Haakaa pump. If you have a long driving commute, or suitable public transpo, you can also consider pumping en route using a battery pack, power bank, or rechargable pump. Most of my links are for Medela products, which have been my sole experience (I own a Symphony and a Pump In Style Advanced (PISA)). But I've heard fantastic things about the Spectra system as well. Note: Insurance provided the PISA, I bought the Symphony off of Craigslist. If you buy off craigslist, be sure to get the Serial Number and call and check with Medela to make sure it wasn't stolen.
You can put your pump parts in a ziploc bag and keep them in the fridge between pumps, but I personally don't like the cold, so I prefer to have several pump sets and make my husband wash them, haha! As far as drying pump parts, I really like the Boon's grass drying pad and accessories. The trees are excellent for hanging the valves and the flowers are a great place to store membranes. If you have your own office space, a small fridge may be a great way to keep your milk stored away from coworker lunches.
For more tips on breastfeeding in general, pumping, supply boosting, etc. You can check out my post Breastfeeding Primer. I also have more tips on pumping in my post about initiating milk supply with a pump. If you've been exclusively pumping and want to transition to breastfeeding as well (or know someone in this situation) I also wrote a blog post on that topic.