I didn't follow an outline at the time, but looking back, here's a rough description of what I did for each paragraph. I'm going to a Ph.D. program straight from undergrad, if that makes a difference.
1. Fluffy intro about how I got interested in research and in my topic in general. For me, this was high school.
2. My first experiences in psychological research working as an assistant in a cognitive lab.
3. Why I transitioned from cognitive into neuroscience, and what I did in the neuroscience lab.
4. Why I transitioned from neuroscience into social, why social is the best fit for me, and how I began my thesis.
5. Details about my thesis and how I plan to present my research.
6. Why the school, the program, and my potential advisor would be a good fit-- how they would help me, how I would help them, the significance of my proposed research.
It ended up being about a page and a half double-spaced, depending on how I tailored it for each program. I basically went in chronological order and told my story up until the present, finishing with future directions and why I should pursue those goals at X university.
6.