Hatch eggs, buy nests and heat lamps that raise your hatch chance, then larger incubators that hatch several at once. Selling eggs for money is itself an upgrade, called Sell Your Soul, and it costs a thousand eggs.
The author's own readme opens by saying it is broken at the moment, and parts of it are: chances and counters do not always agree with each other. Enough works to see the shape, and the upgrade names are good, but do not plan a long evening around it.