The following are examples of the different voting systems used in California, and instructions for writing-in a candidate.
See more information at:
http://www.sos.ca.gov/elections/voting_systems/ca_map_counties3.html

Sequoia
California counties that use Sequoia:
Alameda, Del Norte, Glenn, Imperial, Inyo, Kings, Mariposa, Mono, Monterey, Napa, Riverside, San Benito, San Bernardino, San Francisco, Santa Clara, Santa Cruz, Shasta, Sutter, Tehama, Tulare, Ventura, Yuba

Using the pen provided by the poll worker, mark the ballot by drawing a line between the head and tail of an arrow that points to your choice. To vote for a write-in candidate, write the name of the write-in candidate in the space marked “Write-In.” You must draw a line connecting the head and tail of the arrow that points at the “Write-In” space for your write-in vote to be counted.

REMEMBER: Only write-in votes for qualified write-in candidates will be counted. A list of qualified write-in candidates is available at the poll. If you make a mistake while voting simply request another ballot from the poll worker.

Premier TSX
California counties that use Premier:
Alpine, Butte, El Dorado, Fresno, Kern, Lassen, Mendocino, Modoc, Placer, Plumas, San Diego, San Joaquin, Sierra, Trinty

With a blue or black pen, COMPLETELY fill in the OVAL next to the candidate or issue of your choice.
If you wish to vote for a declared WRITE-IN candidate, find the blank line provided for “Write-In.”
Clearly write the name of the eligible write-in candidate on the blank line. Fill in the oval
next to the write-in line.

Voting System – ES&S Model 100/550/650 and ES&S AutoMark
California counties that use ES&S Model 100/550/650 and ES&S AutoMark:
Amador, Calaveras, Colusa, Contra Costa, Merced, Sacramento, Solano, Stanislaus, Tuolumne

The ES&S AutoMARK allows you to write-in candidates, as well. To cast a vote for a write-in candidate, touch the โ€œWRITE-INโ€ option and a keyboard will appear on the screen.
Use the keyboard to type in the name of a candidate for whom you would like to cast a vote. Once you have entered the name, press โ€œOKโ€ and the name of your write-in selection will appear on your ballot.
Continue making and changing selections until you complete the ballot.

Diebold Optical Scan
California counties that use Diebold Optical Scan with ES&S AutoMark:
San Luis Obispo, Santa Barbara, Siskiyou

With a blue or black pen, COMPLETELY fill in the OVAL next to the candidate or issue of your choice.
If you wish to vote for a declared WRITE-IN candidate, find the blank line provided for “Write-In.”
Clearly write the name of the eligible write-in candidate on the blank line. Fill in the oval
next to the write-in line.

InkaVote
California counties that use Inkavote: Los Angeles

To vote for a write-in candidate,
completely fill in the box provided to the
left of the words “Write-in” and write in
the name of the candidate on the line
provided .

Hart InterCivic – eSlate & DRE
California counties that use eSlate:
Orange (NOTE: Lake, Madera, and Sonoma use DFM Mark-A-Vote Ballots at their polling places, however, they also use the Hart eSlate for accessibility requirements.)

— very similar to ES&S AutoMARK
California counties that use Hart InterCivic DRE:
Nevada, San Mateo, Yolo
Use a blue or black pen to completely fill the box next to your choice. Do not mark more choices than allowed for each contest.
To vote for a write-in candidate, make sure to fill the box next to “Write-In” and write the candidate’s name on the line below.