How do I write a real estate offer "love letter"?

Keep it short and focus on the home, not personal details. Many areas discourage these due to Fair Housing concerns, so ask your agent first.

Unfortunately the National Association of Realtors (NAR) has put a stop to the buyer love letters. They felt it was a way for a seller to discriminate maybe even without intention against others so in order to make offer she more on an equal playing field they have banned us from including them with out offers now!

Consult with your licensed Broker/Realtor about submitting "love letters" with your offer. These letters pose a concern to fair housing law and discrimination. While you may be trying to win the offer in your favor, you may create the opposite effect.

Have your agent see if the sellers are accepting buyer letters this is something that is an option on the residential listing agreement if the seller will entertain these or not. Not all listings/listing agents/sellers will accept these with offers and it does pose a concern to fair housing law and discrimination as David mentioned. That being said if you are going to submit one I would talk about how much you loved their home and certain characteristics and features about it that you liked. I would talk about why you want to live in that particular area too. If you are a first time buyer that might be something to add as well. CA is a very competitive market everywhere but be sure to consult with your agent about your buyer letter. They should be able to help point you in the right direction :)