Pick a name. This doesn't matter, so have fun.
Get Registered Agent service for California. I use Northwest Registered Agent. They will give you an address to use - use this address on all public filings with the state.
Create an LLC on the California Secretary of State website. You want to create the Articles of Organization for a CA LLC. Use your registered agent's address. This address will be public forever. When you create your LLC online, at the Agent for Service of Process section, choose California Regsitered Corporate Agent, and search for Northwest Registered Agent's (#C3184722).
Once you get an email from the state that your LLC is set up, go down to a bank and get a bank account and a credit card for your new business. Any business expense (think: your internet bill, a meal you ate while working, etc...) is deductible from your income. Keep track of all your business expenses in a spreadsheet with the date, the name, the amount, and the rough category of expense. Your CPA will help you use this spreadsheet to get your deductions in order.
Finally, get an EIN for your business. You'll need this at tax-time (the business will file its own taxes; in capitalist America, businesses are persons, remember?). See more about how to get an EIN here.