Several people have mentioned Strunk and AP style guides, and both are reasonably good. Most publishers in the US use the Chicago manual. Take your pick, but ask the prof, or your publisher, which one you are expected to use. It can make a very big difference.

Be aware that the AP style guide is specifically for newspaper usage and actually encourages a lot of things that aren't really good practice in more "formal" work.

I keep all three, Chicago, Strunk, and AP handy and use them frequently - to hold the lid down on the scanner when a piece doesn't want to lay flat.

If you type something in a modern WP program, like Word, when you type three dots "..." it should get "autoformatted" to the single ellipsis character "…" but you don't get that special thrill entering stuff here. My browser displays them so they actually look the same, but three dots is three separate characters, while the ellipsis is only one. In modern typography - or in old stuff actually typeset - it's a single character. Typing three dots is just a "typewriter simulation," or in modern WP it's an "input method." And some old typing manuals did recommend spaces between the dots.

If you really want a "real" ellipsis, the character has ANSI value 133, and you can type "…" to get one in your posts. And yes, if it comes at the end of a sentence, it should have a "period" after the three dots, "…." but that looks ridiculous in typewriter work, so style books varied when people still used typewriters.

Now does anyone want to discuss the difference between hyphen, soft hyphen, n-dash, and m-dash? One of the most exiting topics in typography, since almost nobody ever does it "right."

John