First choose a quality hygienic breast pump.
There are many breast pump out there that while commonplace, are not the best choice. You need an auto-cycling breast pump that does at least 60 cycles and has a closed system like Hygeia, Ameda and Spectra offer. Double pumping increases the prolactin levels as well as save you time. Prolactin is the milk producing hormone.
Next determine your pumping schedule.
A mother of an infant under six months should pump at least every 3 hours that she is away from her baby. That time frame is from the beginning of one pumping or nursing session to the beginning of the next. If your schedule is erratic, you should still pump 3 times per day on an 8 hour work day. Just put some of them closer together if needed to get this time in.
Allow enough time for pumping.
You should allow a full 10-15 minutes for double pumping and then an extra few minutes to rinse your parts and put them away. Do not stop pumping if milk stops flowing unless the time on the clock has passed. Otherwise your body will think you don't need as much milk. A good rule of thumb is that if milk is flowing for less than 10 minutes, pump for 10. If it is flowing past the 10 minute mark, pump for 15. These extra few minutes simulate the non-nutritive sucking your baby does when nursing and is imperative for milk supply.
Don't forget about growth spurts.
Infants nurse more frequently during growth spurts. At 10 days to 3 weeks, the first growth spurt is evident with the baby asking to be fed more frequently. Breast pumps don't cry to be used so we have to intentionally pump more often during this 5 day period. Pumping every 2 hours is best during the baby's third week, sixth week and three month milestone. If this is not possible at work, pump at home after feeding the baby at least three extra times per day. Don't worry about the amount of milk you are extracting. This is more for stimulation than extraction, indicating to your body that your baby is about to grow and will need more milk.
Maintain your breast pump.
Professional grade breast pumps like the Hygeia EnJoye, Spectra S2 have systems that are dependent on maintaining suction. Replacing breast pump valves and filters every six to eight weeks is essential for keeping your breast pump working at it's optimal level. Keep breast pump parts on hand and replace on schedule or more often if you notice evidence of decreased suction or damage to your parts.
With good information prior to embarking on full time pumping or working and breastfeeding it is entirely possible for you to maintain a healthy milk supply.