Hunger Cues. You'll learn your baby's various cries and cues over time. In the meantime, some hunger cues are fairly universal. While babies cry for all kinds of reasons, if it's been awhile since her last feed, and she begins fussing, puts her hand to her mouth, sucks a lot, or roots her face toward anything that it touches, she's hungry. Feeding at the onset of fussing can prevent the "frantic baby" later.
Look for hunger cues. Babies are fairly adept at responding to hunger and if we pay attention, we can start recognizing their hunger cues. Waking, looking alert, lip smacking, making sucking motions, bringing hands to mouth, nuzzling against breast, and squirming are all signs your baby is ready to feed again. Crying is considered a late sign of hunger. Pretty soon, you'll have mastered your baby's hunger cues.
Experience. Little babies will root, turning their head and opening their mouths in a movement of looking for the breast. Tired babies tend not to make eye contact. It never hurts to try a feed. As you get to know your baby and his or her cries, you will become adept and knowing if baby is tired or hungry.
Infant Sleep. Newborns typically sleep 16-17 hours a day, waking every 2-4 hours both day and night, with increasing sleep periods as they get older. You may notice your baby sleeps slightly more just before a "growth spurt." the drowsy infant may appear to have heavy eyelids, look a bit dazed, have delayed reaction to stimuli, and may bring their hands to their face more as though to rub their eyes.
Read babies signals. First and foremost, do not equate sucking movements to hunger. Babies are prewired to suck 24/7. My moms find it helpful to set a day pattern: 2 hr rest period/ immediate feeding/ body maintance followed by play until tired and then place in the crib for rest. Since feed/maintain/play lasts about an hour, hunger is unlikely. I let baby wake and set the time night feeds. A good pattern works.