Divide a regular three-meal schedule into six to eight smaller ones. Have snacks between meals. Establish a pattern of eating meals and snacks at definite times. Stick to the schedule, even when you are not hungry. Keep snacks handy for nibbling.
People tend to eat more when food is readily available.
Rely on foods you really like at times when your appetite is not good. Substitute high calorie, high protein drinks when foods are unappealing. Prepare foods that have a pleasant aroma. This can help stimulate your appetite. What most people lack when they are ill is not advice, but an appetite.