How to stay motivated to get fit?

For years now I've told myself that same line over and over again.

"I'm going to get toned and become healthy, no more junk!"

I can't seem to get passed the first week of working out and eating right. I always sulk into a box of cookies and bowl of ice cream after my motivation is non-existent. I end up missing the sugary foods I'm so used to eating and completely lose focus. Months go by and I get the motivation again, then right back to losing motivation.

I honestly don't know where to start. I want results and when I don't see them quick enough, I quit. How do I stay motivated? Any meal plans or workout you suggest?