
To begin with, not all publishers want submissions in the same format. Clearly, it would be a daunting task to list every possible format. Instead, only a few will be described. Regardless of what's described here, always consult the publisher's guidelines and follow those carefully.
For all works, the second and all subsequent pages should have the following listed at the top of each. The title, a slash, and the last name of the author should be in the upper left corner. The page number should be in the upper right corner. Most word processors can do these for you as an automatic header once you set up the first occurrence.
Some publishers want a blank line between paragraphs. Almost all publishers want either a blank line between paragraphs of different scenes or times within a chapter. Many will accept a series of three asterists on the line separating different scenes within a chapter as it makes the change even more clear.
When you reach the end of the story, you should drop down two lines from the last line of text and center the word "end". It doesn't hurt to offset it by adding some asterisks on each side of it, either.
Another major difference is that they usually don't want a header showing the title, author's last name, and the page number since that would be copied along with the rest of the manuscript and make the overall page numbering task difficult for the publisher. When in doubt, ask the publisher using this method about those.
As well, they don't want a blank line between paragraphs unless it's to denote a major change of scene or time within a chapter. Using lines with asterisks to separate changes of scene or time also appear to be acceptable in this format. Again, ask the publisher when in doubt.
One of the problems with ASCII is that tabs, double-spacing, and other features of word processors don't show up or convert readily. However, the ease of loading the electronically submitted manuscript permit the publisher to allow for this as, once the ASCII file is read into the publisher's word processor, it can be returned to double-spacing very easily. However, the writer must be aware to begin with that some features are strictly forbidden as they cause more than their share of grief for everyone. One of those features to avoid like the plague is "smart quotes" as it is known in some word processors. Thought the smart quotes look great when printed out, they aren't converted to ASCII as quotes. ASCII documents with those inside are nearly impossible to read clearly and require major editing. Many publishers will not accept submissions with problems such as those caused by smart quotes so the writer is well advised to turn that feature off in the writer's own choice of word processor.
As well, italics and other features often don't convert. For those, consult the publisher's guidelines to learn how the publisher wants words needing special treatment to be marked when submitted in ASCII.
As well, there are differences in how electronic submissions should be sent. Some publishers want the submission inside an e-mail letter. Some want it attached as a file to the e-mail. Some won't accept it as e-mail. They only want it on diskette sent by regular mail. Again, the publisher's guidelines must prevail if you want your work considered, so follow those as best you can.