How can the efficiency of an inclined plane be increased?

Answer 1

Use a lubricant

Answer 2

Efficiency is the ratio of power output to power input. It is not the ratio of forces or distances. You can move a load using less force by reducing the gradient of the plane. But what you gain in reduced force you lose in having to travel a greater distance to raise the load through the same height. There is, therefore, no net advantage.

The only way to increase the efficiency is to reduce the friction. This can be done by lubricating the plane, or load (or both), or by placing rollers between the load and the plane - so that there is rolling friction rather than sliding friction.