NC-110

The NC-110 form has information about you and your name change. It's required for all California name changes. If you're changing multiple people's names, you'll need a separate NC-110 form for each person.
Start by filling out the header as detailed here, and then do the following:
Where it says "Attachment", write 1 of 1, or change that as needed if you have multiple NC-110 forms.
Under field b, check 
Self if you're changing your name, or 
Other if you're changing someone else's name.
In field 1, write your current legal name
In field 2, write the name you want to change it to
In field 3, write your date of birth and check the correct box about your age
In field 4, put the county and state where you were born
In field 5, check the box corresponding to your AGAB
In field 6, write your current address
Under field c, enter the reason for your name change (e.g. "To conform to my gender identity (female)").
Under field d, select your relationship to the person whose name is being changed. Select 
Self if you're changing your own name.
Under field f, check the boxes corresponding to your current legal situation, and then print your name, write the current date, and sign.
Under the text that says "Each petitioner must sign", write the date and your name, and then sign.
Example
Here's what your form should look like once it's finished (Everything I added is in red for emphasis. Use black when you're filling your form out):