How to run AC units efficiently at home or office? PART 1

How to save electricity?
How to keep your current bill under YOUR control?
How do you set your thermostat to be comfortable yet spent less on electricity?
How to make your AC think like you?

These are common questions faced by all.
But a very few take the trouble of understanding it.

===================================================================================
In India atleast, it is not very uncommon to see a client buying the best TV at a higher price, but buying an AC that is cheaper! By watching that TV he does not spend much elctricity additionally: But he is going to spend more on elctricity by running the AC. Hence it makes a lot of sense to buy an efficient AC. Still he chooses to buy a cheaper unit! It is ironical. Is it not? I am not attempting to change one's buying preferences, which I can't. I can only tell how you can run any AC atleast effectively! '
=================================================================================== contd....... in Part 2