1. Know some design history; be aware of--but not a slave to--aesthetic trends; and stay open to ideas from your design team to keep the work fresh.
2. Keep in touch with your network (former professors/mentors, fellow ADs, designers, photographers, stylists, technicians, writers). Your contact list is one of your most marketable assets.
3. Understand the technology that helps you produce your work. Your vendors and subcontractors (printers, prepress, retouchers, set builders, I.T. consultants) are your best resource for learning. Show them respect. Ask questions. Learn to speak their language.