Use single rather than double quotes. But it’s okay to use double quotes when you’ve got a nice quote in a large font size, like in a PowerPoint presentation or a proposal title. Because they look prettier.
If you’ve got a quote within a quote it should go like this:
Ify said, ‘Is it true that Padders asked “If you’re a Catholic, does that make you a Christian?” the other day?’
Punctuating around quote marks
Pretty much the same rules as when you’re punctuating round brackets.
So when the quote you use is part of a longer sentence, the full stop (or any other punctuation) goes on the outside:
Harry said it was ‘beautifully written’.
When the whole sentence is in speech marks, the full stop should go on the inside (even with the ‘Harry said’ at the beginning – and notice the cap on ‘It’):
Harry said ‘It was beautifully written.’ Or ‘It was beautifully written,’ said Harry.
Curly or straight?
Curly quotes (‘ ’ “ ”) look nicer, so if you’re writing for print, go with these. Word should put them in automatically, but if straight ones show up instead (' "), which they do sometimes, generally if you’ve copied and pasted something, see Useful keyboard shortcuts on how to fix them.