A basic knowledge of aesthetics is a pre-requisite when you set out to pursue photography. While training your lens on a subject, your sense of composition, space division and light will make all the difference. You should know how the picture will look before you press the shutter, i.e. have a clear picture of what exactly you want the frame to convey, in your head.
Technical know-how is very, very important. You should know how to operate a camera and lighting equipment. You must have a thorough knowledge of different kinds of lighting, such as studio lighting and outdoor lighting, and you must study natural light. A familiarity with how to operate computers is a must for post-production work. It helps if you also have a basic knowledge in printing technology. You can then work towards a picture keeping in mind in which form it will be reproduced, say on hoardings or newspapers and magazines.
Lateral thinking is a must. Keep your mind free to explore other options if a photo shoot is not working out the way you had initially planned. Since photography is a creative profession, always try to think out of the box. That gives you an edge over others.
Always keep yourself abreast of the latest photography equipment that hits the market. Look up the Internet, subscribe to newspapers and magazines to check out the works of other photographers. You should be patient during crunch situations.