Deliver a product of consistent quality, at your highest level of ability.
Be able to deal with the ups and downs of getting paid, mostly not on time. After your business becomes established there will be a more consistent cash flow and you can build a financial cushion. However to begin with, the best way to handle the feast and famine situation is to keep out of debt. If you leave school with debt, take any job you need to in order to pay it down as quickly as possible, and then stay out of debt to the greatest degree you can.
Recognize what helps you to be creative, what times of day are the best work hours for you, what environment works best, and then try to create that environment and work within that schedule.
Be able to diminish the distractions and focus.
Lastly, build a solid network. The support of family, friends, clients and acquaintances can help you on both a business and personal level!