This is a small thing but being aware of it will help your writing appear more professional.
I've written in the past about the need to have a consistent writing style. Nothing shouts 'amateur' more than a mixture of American and British spellings on a website, the same word spelt in different ways or, worse still, a variable treatment of the way you spell your own company's name. (It does happen.)
A common area for written content to become unkempt is in the use of quotation marks to mark speech and to emphasise words. I see this most often in blog posts. So let's go to school on that.
The most common method for directly quoting someone's words is (as everyone knows) to surround the speech with quotation marks. Where it gets messy is in the choice of single or double quotation marks:
"Look, there's a well on top of that hill," said Jack
'Let's fetch a pail of water,' said Jill.
Both are correct (though not both together). As a general rule, double quotation marks are used in American English, single quotation marks are used in British (and Australian) English.
The only time you should mix the two types of quotation mark are for a quote within a quote, in which case you use the alternative for the 'inner' quote:
"Then Jack said, 'There's a hole in my bucket', and promptly fell down the hill," laughed Jill.
(There are various rules about where to put commas and full stops at the end of a spoken sentence – it varies for fiction and non-fiction, and in the American and British contexts. A topic for another day.)
The same approach applies to emphasising a word or phrase in your text, in that you can use either 'single' or "double" quote marks to do this. For clarity's sake, it's best to choose the emphasis style that 'opposes' your speech marks. So, if you're using double quote marks for speech, use single quotes for emphasis, and vice versa.
"You call that 'water'?" said Jack. "It looks more like mud."
'You call that a "bucket"?' said Jill. 'It not much use with a hole in it.'
It's your call
Unlike the use of American or British spellings – in which there are rules to abide by – the choice of quotation marks is largely up to you. Probably in the US, or for a US audience, you would want to use double quotes for speech (and single for emphasis) because that's what they are used to. In Australia, at least, my view is that you can go either way provided you are consistent. My personal preference is the American style – I just like double quotes – so that's what you'll see on my website and in this blog.
Quote and emphasise away.