When Ewan was only a few days old he began doing what is known as "rooting", that is, searching for a nipple when hungry.
He would open his mouth and touch it to any exposed skin on anyone who was holding him. He would pull away and touch in a different spot very quickly like he was pecking around. My sister was holding him when he was about a week old and she said it felt like he was giving her little kisses on the cheek, because he was rooting around on her face. It was really cute and my husband said he looked like Pac-Man with his mouth open like that. It was really easy to see when he was hungry because he would just do his Pac-Man thing.
He had quickly associated nursing with sucking on skin, so he would try to suck on whatever skin was around.
Later, at about 6 weeks to 3 months, he would lean himself over and try to eat my arm. It was summer, so I was always wearing short sleeved shirts.
At about 4 months he started standing on my lap and squatting down to get his mouth near my breasts. He knows where he wants to be!
Most recently, since he has learned to hold things and pull them to himself, he will grab my hair on both sides of my head, pull himself to my face, and try to suck on my lips. Really. Sometimes, he tries to suck on my nose or my cheek.
It is usually very obvious that Ewan is hungry, so that makes feeding on-demand easy as long as I pay attention to him.