What actions can manufacturers take to make transformers more efficient?

A manufacturer has various options to lower losses. To lower no-load loss, the manufacturer can change the core material. Another option is to use thinner laminates, which reduces eddy currents in the core. Or the manufacturer can reduce the induction in the core. To reduce load losses, the manufacturer can choose for a conductor material with higher conductivity (copper instead of Aluminium). Or the resistance of the winding can be reduced by choosing a larger conduction cross section.