In certain contexts, I know that you can use the generalised noun.

Ambition is the desire for personal achievement.

We need exercise.

Technology has experienced vast improvements over the past decade.

(Did the word 'vast' make the generalised noun 'improvement' unusable?)

Time is money.

Fluid can move around freely.

He is a man of sorrow.

Appearance is deceptive.

Skill is the ability to do a job well.

Are the above usage of generalised noun correct?

What are the conditions that must be fulfilled to use generalised nouns?

Could you please list out some more examples of usage of generalised nouns?
Technology has experienced vast improvement(s) over the past decade. (Did the word 'vast' make the generalised noun 'improvement' unusable?-- No; 'improvement' is fine there. However, you must decide whether you are speaking of the general process of improvement or the many individual improvements that have been made – that is where the choice of words comes in.)

Appearance is deceptive.-- Usually: 'Appearances are deceptive'.

Are the above usage of generalised noun correct?-- Yes.

What are the conditions that must be fulfilled to use generalised nouns?-- You are speaking of the general condition/process/quality/etc. rather than specific instances of them.

Could you please list out some more examples of usage of generalised nouns?-- You have given plenty already. Their numbers are legion.
So,

We need exercises, such as swimming,jogging and running.

We need exercise, such as ...

Is the second one not acceptable?
Students: Are you brave enough to let our tutors analyse your pronunciation?
Not really; we usually use 'exercise'. You must simply learn, case by case (as with protein and vitamins), which nouns are normally used countably and which uncountably. There are no rules; there are only general perceptions.
Mister MicawberNot really; we usually use 'exercise'. You must simply learn, case by case (as with protein and vitamins), which nouns are normally used countably and which uncountably. There are no rules; there are only general perceptions.
How I wish that English was simpler!

Anyways, thanks for the help!