Colons are one of the most misused pieces of punctuation I encounter. In short, use a colon to introduce a list, but not if the list reads like a complete sentence (it does not matter if this sentence is broken down into bullet points).
- When to use a colon (the introduction to the list is a complete sentence): Last week’s top news stories featured a diverse group of people: Barack Obama, Anna Nicole Smith, and three naughty astronauts.
- When not to use a colon (many writers put one after “such as”): The top news stories from last week featured a diverse group of people, such as Barack Obama, Anna Nicole Smith, and three naughty astronauts.
As with all of the suggestions I provide on this website, some style manuals offer different guidance. Most of what I recommend is based on The Chicago Manual of Style. The Microsoft Manual of Style for Technical Publications, for example, mandates colons (or a period) before every bulleted list.