The key to motivation is to surround yourself by people who support or help you with your goals. Another key is to design your life and your environment in a way which stimulates your quest, your desires and what you want to reach and achieve in life. Motivation is your emotional fuel. Without it, there is little movement. The key again is to find around you people, individuals, sources of energy and inspiration which stimulate you in a positive way.
Another key to motivation which is more "internal" has to do with clarifying your choices. Conflicting interests in us often make us shift directions. You go right one day, left the other day, neutralizing your efforts that way. The key is to have a consistent movement by clarifying your goals and dealing with conflicting interests before you even start moving. Nurture and nourish all aspects of your life. Give attention to all aspects of your existence, so that your personal foundation stays well balanced.
Enjoy!