Do not use full stops in abbreviations, or spaces between initials, including those in proper names:

US, M&S, WE Weber, WH Smith, etc.

Use all capitals if an abbreviation is pronounced as the individual letters: BBC, VAT, etc; if it is an acronym (i.e. pronounced as a word) spell out with all capitals (NASA, NATO, etc.) unless it can be considered to have entered the language as an everyday word, such as awol, laser and, more recently, asbo and sim card.

The first time an institute or machine is mentioned it must be written out in full with the acronym following in brackets (note that this does not always apply when writing for the CERN Courier – see individual entries). After the first mention, it can be referred to by the acronym throughout the article:

The Large Hadron Collider (LHC) is in Geneva, Switzerland. Scientists at the LHC...

Only capitalise the first letter of each word: 

He works for the Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) at CERN. 

Not

"He works on the COmmon Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) at CERN."