Efficiency goes up when less of the energy supplied is wasted. To increase efficiency, we reduce the energy dissipated to the surroundings so more of it is transferred usefully.
Friction is a major cause of waste in machines, so lubrication increases efficiency. Streamlining a vehicle reduces air resistance, and using smoother, well-fitting moving parts reduces friction as well.
Electrical devices waste energy by heating wires and components. Using thicker wires, which have lower resistance, wastes less energy. An LED lamp transfers far more of its electrical energy to light than a filament lamp, which becomes very hot, so replacing filament lamps with LED lamps increases efficiency.
Thermal insulation increases the efficiency of a heating system, because less energy escapes from the building. No method can make a device 100% efficient, because some energy is always dissipated.