Somewhere in one of my comments, Sally has asked me for some more information about dashes and ellipses. Do, therefore, please blame her for the following rather boring post.
It's difficult to give exact rules for the correct usage for either the dash or the ellipsis as much depends on house style: the most important rule to remember is to be consistent. Choose one way and stick to it throughout your work. Use a "find and replace" to locate all examples once you've finished, just to ensure your consistency. And once you've done that don't get into a lather about them, as so much depends on the editor or publisher you're working with.
For the ellipsis, the usual convention is that it has a space after, but not before, or between each individual dot; and that if one ends a sentence, then you add a full stop so you get four dots in a row, and that full stop will naturally necessitate that a capital letter follows. So we use ellipses like this in the middle of a sentence... and like this at the end.... Ellipses indicate a trailing off (for example, in speech), rather than an interruption or abrupt halt, for which you use a dash.
Some houses prefer no spaces at all on either side of their ellipses and some (although happily, these are in the minority as I think it looks awful) prefer a space either side. I'm not sure which one I think is worse.
Dashes are more tricky. House style dictates, as usual. First rule is to remember that they are NOT interchangeable with hyphens, and that you need to show the difference between dashes and hyphens, usually by using two hyphens without a space between them to indicate a dash.
Whether or not you use a space either side of your dashes, like this:
text -- text
or don't, like this:
is up to you and the dictates of your style guide. I usually default to the latter, with no spaces, as it's what is preferred by the Chicago manual, which is what most American publishers default to when they're unsure.
Then you have to consider em- and en-dashes: the en and em refers to how much room they should take up on the line. The choice here is, once again, mostly a matter of house style although strictly speaking there are specific situations when each one should be used. If I'm in any doubt I usually default to the em-dash throughout rather than the en, as it's easier to differentiate from hyphens and so leads to a clearer text.
Finally, I'd ask everyone to use as few dashes and ellipses as possible as otherwise your text is going to look like the punctuation-spider has been sick all over it. Not a pretty thing, and very distracting to the reader.
There. I just hope Sally is grateful. After all--she asked.