Here in DC the money is made in the winter months not in summer. Get to know the streets inside and out..i.e. allies, parks , ect so you can get from point A to point B with the least amount of effort. Get to know the buildings and where you may have to pick up and drop off at. i.e. front desk, secretary, mailroom, ect. Get to know the companies main clients so you can get the package out of their face ASAP. Main thing you don't want is to be the reason the company loses a 10-20 per day client. Always carry tools, pump and extra tube(s). Eat well at the end of the day to restore the carbs you burn. Believe me you'll notice it if you don't constantly refuel during the day and you'll know the next day if you decide to go to the bar drink beer and eat chips after work.To each his own but I NEVER consumed anything that could/would alter my senses in any way when working. Here in DC you need to be ALERT especially with cabs and rush hour. If not you WILL get hit. Getting hit....it's not if it happens it's when it happens. Stay alert to keep that when has minimal as possible.
Have fun and remember there only a handful out there that are hardcore vets. Most couriers don't last 2 weeks. Some a year or 2. Then a small majority that make a career out of it. Watch them and learn if you plan to do this a while.