rice cereal

Hi ladies. I'm not looking for anyone's opinion of if they support rice cereal or not. So please don't bring that in your comments. My baby is 4 months old and had her appointment today. She hasn't lost weight but isn't gaining super fast. The doctor recommended rice cereal, so I feel good about giving that to her. But how do you ladies feed it to your babies, and how about the ratio of BM to cereal. Thank you in advance.