If you homeschool in California under the private school provision, now's the time to file your PSA (Private School Affadavit, formerly known as the R-4) online. This is the document that registers your homeschool as a private school.
This page at California Homeschool Network will walk you through the PSA step by step.
Here's the CA Dept. of Education's link to the PSA itself. Start here to fill out your online registration. The filing deadline is October 15th. If you miss that deadline, you may submit a hard copy "Statement in Lieu." See the CA Homeschool Network link above for instructions.
After you submit the online form, print out a hard copy for your records. This will have a confirmation number on it to prove you submitted it to the state. I follow the CHN's advice and keep a folder containing my PSA hard copy next to my front door, along with a copy of the pertinent sections of the CA Education Code. In a separate folder are the other records a private school is required to keep on file (but not required to show to public school personnel such as truant officers).