The specific improvements in energy production will vary from energy source to energy source. For example, the improvements that may have taken place for hydropower generation may not be applicable for thermal power generation. However, there are some generic improvements that apply to all the energy sources. One of the measures to reduce the production cost is the use of high efficiency equipment. For example, more efficient turbines will convert more power from falling water or superheated steam to useful energy. Similarly, improvements in fuel quality (say, the use of anthracite in place of peat coal) will improve the production of energy. Automation of production has also helped us reduce the production cost. For example, generating only the energy that is needed (instead of constant production) to fulfill the demand, will help us tackle the cost of production. Significant improvement have also taken place in energy transmission to cut down on the losses.
Hope this helps.