Capital letters are creatures of fashion. The Victorians used capital letters far more often than we do now, when style guides for papers like The Economist and The Daily Telegraph recommend a light touch with capitalisation. This is at odds with a lot of business writing I see, which uses capitals to emphasise points the writer thinks are Important and Valid. This is Wrong. Sorry, wrong.

I prefer the light touch approach to capitalisation because it preserves the readability of your text. Too many capitals, or capitals in unexpected places, merely confuse the reader.

That is not to say that you shouldn’t use capital letters. Far from it.

Always

Use capital letters:

• At the beginning of a sentence
• Proper names (Mary, John)
• Places (Newcastle, Durham, Trafalgar Square)
• Countries (France, Scotland)
• Organisations (British Museum)
• Months, festivals etc (Christmas, December)
• Events (First World War)
• Acts (Data Protection Act)
• Titles of books (Alice in Wonderland)
• Trade names (Cadbury, Skype).

Sometimes

Most people expect to use capitals in the circumstances in the list above. Where it gets a little more complicated is with job titles. I prefer to go with Hart’s Rules and The Economist and use capital letters with job titles only when they’re to the left of the holder’s name. For example:

• The Head Teacher, Miss Dunn, altered the timetable.
• The Head of Equestrian Studies, Bill Murray, bought 16 new horses.

In all other instances, job titles are lower case, so you would say:

• Miss Dunn, who was the head teacher, altered the timetable.
• The head of equestrian studies arranged the sale of 5 badly behaved horses.

Never

In the text
Don’t add capital letters to try and add importance to what you write. It runs the risk of looking a little desperate: that you are so unsure of the quality of what you’re writing about that using capital letters is the only way you can think of to make it sound even vaguely impressive.

Here’s an example:

• The client asked us to design Annual Reports, Newsletters, Logos, and all other Marketing Material.

What you should write is:

• The client asked us to design annual reports, newsletters, logos, and all other marketing material.

Colons
Another situation where the capital letter has crept in is after a colon. This is understandable if you read many American websites, as to use a capital letter after a colon is the convention there. However, it is not in the UK. I suspect it won’t be long before sheer volume of usage makes it normal practice, but for the moment, if you’re in the UK, observe the UK convention.

• Point 1: This is wrong if you’re in the UK
• Point 2: this is right if you’re in the UK.

These are the most frequent usages where you’ll need to think about capitalisation. If you want to read more, The Economist’s style guide is an excellent read.