Feed oneself/an animal on X literally means a person or animal lives by eating X.
Cattle feed on grass. We feed cattle on dry grass.
"You can't feed yourself on the day before yesterday" means:
You can't live or sustain yourself (artistically) by trying to get/imitate something
that is not very old like the day before yesterday.
The writer metaphorically compared the day before yesterday to something that people eat.
"It's ground which has been swept dry." means:
Many artists already tried and used all the artistic features of "the
day before yesterday" and there is nothing left for you to get. Nothing very artistic or creative can come out there.
"Ground swept dry" could be better understood if you would imagine a grassland in Serengeti. If all the herds of buffaloes, zebras, and gazelles, etc. sweep through a grassland, there is no fresh grass left to feed on for any other herbivorous animals that come late. They should move on to another grassland to survive. If they stay there, they will die out.
The writer is emphasizing that a ground that has been swept dry and the day before yesterday are not the place where you should stay and try to get something. You have to go back further to the past where the ground has not been swept dry yet by others.