An acronym is a pronounceable name made from initial letters, eg Unesco (for the United Nations Educational, Scientific and Cultural Organization), Nato, Aids, Ucas.
Acronyms are written with initial caps only.
Names of organisations, etc, should usually be written out in full at first mention.
If there is going to be further mention, the generally accepted acronyms or initials should follow (in brackets): the Trades Union Congress (TUC).
On subsequent mentions, use the initials only: TUC. Better, to avoid littering your copy with initials, refer to the organisation on subsequent mentions by its function.
Thus the Independent Television Commission would become the commission (note the lowercase c here).
But some familiar organisations may be referred to by initials or acronyms throughout: BBC; IRA; RAF; Aids.
Also, use initials throughout when writing for a specialist readership (eg in a specialist business magazine) about an organisation with which it can be assumed to be familiar.
Some titles are clearly too cumbersome to use in full at all.
In such cases, use the acronym or initials with an explanation: Aslef, the train drivers’ union; BSE, mad cow disease.