How do you keep yourself motivated?

Easy. The knowledge that if I don't sell, I don't live the life that I want. In other words, (besides the glory, winning a challenge, recognition, etc that goes along with sales) money, the bottom line for any salesperson.

Establish an accountability group that will help you think big, remind you of your goals and push you when you start to slip.

Let's distinguish between motivated and focused. Goals, accountability, and the desirability of three squares a day seem to me to be more like focus issues.

Motivation - self-starting, genuine interest, joy, pride, and all that - is born of passion, the love of what one is doing for its own sake. If the love isn't there, the enthusiasm can seldom be intrinsic and real. That's when focus techniques get to be really important for success - maybe even for survival.