An advocate is somebody who seek to get the best out of you, and also a person who seeks to get the best services for you. An advocate, overall, seeks to enable you to reach your full potential without you suffering in the process.
One example: an advocate for an autistic child will seek to obtain the best possible educational placement for that child. If the child is into science, and is good at it, a successful advocate will be able to find a program which emphasizes the sciences, while allowing the autistic child, when stressed, to cool off somewhere without fear of punishment. An optimal program will also assist the child, in a gentle and nonstressful manner, to successfully socialize with his/her peers, teachers, and family members.
To self-advocate is to advocate for yourself, rather than have someone advocate for you.