About the program
Full information about the NSF GRFP can be found here. I applied for it at the same time as I applied to neuroscience PhD programs. It's a really great opportunity- they take about 2000 fellows each year spanning the sciences (excluding clinically focused work).
Mallory Ladd’s website also has some excellent advice on the NSF GRFP
Applications are usually due in late October, so I recommend starting them over the summer. Feel free to reach out to me if you have questions! Good luck.
My application materials
In case they are helpful for your application, here are my submitted materials, minus my transcript:
Personal Statement
Research Proposal
Feedback
CV