When to use dashes and parentheses? Sometimes it seems like they can both be uses for the same purpose.
It depends how you want the sentence to flow, but these are the basic rules.
Parentheses (Forgive me if I use brackets but I'm English...)
Parentheses are used to bracket information that is not vital for the flow of the sentence.
For example, I could say "My printer has broken because I hid it in the oven" without any extra information needed to expand the sentence.
However, if you wanted to expand the sentence and put some unnecessary information in, then you would use brackets.
"My printer (the HP 7520 model) has broken because I put it in the oven"
The brackets aren't a necessary part of the sentence, but sometimes they're nice to have to give extra info.
Brackets can also be used in a more informal way. For example, in a text, when the reader is often known to the writer.
"I'm off to the dog shelter (Katie's sooo excited) so we can buy a new dog"
'Katie's sooo excited' is more of a comment, so I personally wouldn't use dashes around it as it is not needed to interrupt the flow of the sentence.
Dashes are used in a way when you want to bring attention to the fact that, for example, Andy is the man that you have loved forever and it is only now that you have realised.
"As the flames licked at the cage, Andy - the sweetest man I know - leapt at the mesh box full of pups."
Basically, the rule to remember when using dashes is that you are highlighting the note and not simply leaving it as a comment or side note. Also with brackets you always need a pair but woth dashes you could use one or two.
"There was one thing distinguishing this hellhole of a room from being a prison cell - the lack of a key"
Hope this helped :)