Question

suggest 3 major for the conservation of energy resources

Answer 1

thermodynamics 1 law is your answer

Answer 2

Energy is the basic requirement for economic development. Conventional sources of energy like petroleum, coal, firewood, natural gas have long been in use. Be it agricultural sector or industrial sector they require energy sources to remain operational and to ensure production. With the increase in population, rising demands, greater industrialization, increased consumption, changes in transportation our energy requirements will increase hence their is an urgent requirement to look for and tap non conventional sources of energy like solar energy which is called Energy of Future, wind energy, geothermal  energy.

We have to judiciously use our limited sources of energy and conserve them.

a. For instance, by using energy saving devices, switching off electricity when not in use we can contribute our bit in conserving non renewable sources of energy and must make use of renewable sources of energy for our requirements.
b.We can for example can make us of solar heater, cookers, use biogas for cooking and lighting. In this way we can make a difference as energy saved is energy generated. 
c. Prefer to walk or cycle foe short distances, using public transport systems instead of individual vehicles.