An abbreviation is a short form of a word that is generally used to save space. Abbreviations are thus quite useful for programmes, agendas, invoices and other documents with non-standard formats in which space is a concern. In contrast, they should be used sparingly in the body of a text. For instance, you do not need to abbreviate terms that appear only once.
Abbreviations prevent unwieldy repetitions. However, when used indiscriminately, they can be confusing and lead to distracting inconsistencies in a text. When introducing an unfamiliar abbreviation, it is thus a good idea to use the full term on first mention, followed by the abbreviation to be used thereafter in brackets. Likewise, in documents with many abbreviations, consider including a key at the start or end.
Remember that terms used in titles should not be followed by their acronym or initialism. Use just the acronym or initialism in question if it is sufficiently familiar. Otherwise, use just the full term. For example:
The EU approves the UOC's participation in a working group to foster innovation in active and healthy ageing [not
The European Union (EU) approves…]