To Identify methods of reducing friction, we first have to understand what is the cause of friction. There are two reasons behind friction:
Whenever two surfaces come in contact, then the temporary bond's start forming between them, which resist the movement between the surfaces. Higher the area of contact, larger the number of bonds, higher the value of friction force.
The abnormality/Roughness of the surface, more rough the surface is, higher the friction.
Value of friction force is proportional to the Normal contact force. Higher the Normal force, larger is the friction
Methods for Reduction friction:
Make the surfaces little more smoother. Rough surfaces produce more friction and smooth surfaces reduce friction. Note: Making surface highly smooth will also increase the friction, as large number of bonds will form then.
Lubrication is another way to make a surface smoother. A lubricant is a slippery substance designed to reduce the friction between surfaces.
Make the object more streamlined. A streamline shape is one that allows air or water to flow around it easily, offering the least resistance.
Reduce the Normal force acting between the surfaces in contact. The stronger the Normal force acting on the surfaces, the higher the friction.
Reduce the contact between the surfaces, so that less number of bonds will be formed. Spheres are the best shape for reducing friction because very little of a spherical object is in contact with the other surface.