Do a spell check – it won't find everything, but it will help you clear up the obvious errors. See some examples of things spell check won't spot.
Print it out – you can check thoroughly on screen first, but it's amazing how mistakes can leap out at you once you see things in print. You can also check for consistency much more easily if you have a hard copy in front of you.
Concentrate – if you just give it a quick read through, you'll see what you want to see. You need to consciously look for errors.
Don't try and check everything at once – you'll need to make several passes looking at different things, such as sense, spellings and consistency.
Do separate checks for significant items – for example, check the main text, then look at headings/sub-heads, numbers (page numbers, lists, numbers in the text and so on), names/titles etc.
Check for consistency – look at typeface/font sizes, use of capitals, preferred spellings eg organisation or organization, numbering systems and so on.
Punctuation – for example check for missing full stops (have you used them consistently at the end of bullet point lists?), brackets and speech marks (are they at the beginning and end of relevant text?), hyphens (co-operate or cooperate?), apostrophes (in the right places?).
Look out for homophones (words that sound the same but have different spellings) eg their and they're, your and you're, aloud and allowed, steel and steal etc.
Don't take anything for granted – call phone numbers and test web links to make sure they're correct.
Take extra care over the big things – for example main headings, place names, people's names, significant facts and figures – anything that's likely to cause embarrassment or upset someone if you get it wrong.