Baby knows how much to eat. Do not force baby to eat it all. When baby cries, it does not always mean hunger. Baby might need a diaper change or to be held or cuddled. Learn which cry means hunger.
Babies have growth spurts.
They will eat more often when growing. It is a myth that cereal will help baby to sleep all night. Don't start cereal or other solid foods too early. Throw out leftover formula after each feeding. It should not be reheated and used.