The most important feature of a good PostScript file from the standpoint of including it in another document is an accurate bounding box comment. Every well-formed PostScript file has a comment describing where on the page the graphic is located, and how big that graphic is.
This information is given as the lower left and upper right corners of the box just enclosing the graphic, and is thus referred to as the bounding box. These coordinates are given in the default PostScript units (there are precisely 72 PostScript units to the inch, like TeX big points) with respect to the lower left corner of the sheet of paper.
To see if a PostScript file has a bounding box comment, just look at the first few lines of the file. PostScript files are standard ASCII, so you can use any text editor to do this. If within the first few dozen lines there is a line like
%%BoundingBox: 25 50 400 300
(with any reasonable numbers), chances are very good that the file is Encapsulated PostScript and will work easily with Dvips. If the file contains instead a line like
%%BoundingBox: (atend)
the file is still probably Encapsulated PostScript, but the bounding box is given at the end of the file. Dvips needs it at the beginning. You can move it with that same text editor, or a simple script. (The bounding box is given in this way when the program that generated the PostScript couldn't know the size in advance, or was too lazy to compute it.)
If the document lacks a `%%BoundingBox:' altogether, you can determine one in a couple of ways. One is to use the `bbfig' program distributed with Dvips in the `contrib' directory. This can usually find the correct bounding box automatically; it works best with Ghostscript.
If the comment looks like this:
%%BoundingBox: 0 0 612 792
the graphic claims to take up an entire sheet of paper. This is usually a symptom of a bug in the program that generated it.
The other is to do it yourself: print the file. Now, take a ruler, and make the following measurements (in PostScript units, so measure in inches and multiply by 72): From the left edge of the paper to the leftmost mark on the paper is llx, the first number. From the bottom edge of the paper to the bottommost mark on the paper is lly, the second number. From the left edge of the paper to the rightmost mark on the paper is urx, the third number. The fourth and final number, ury, is the distance from the bottom of the page to the uppermost mark on the paper.
Once you have the numbers, add a comment of the following form as the second line of the document. (The first line should already be a line starting with the two characters `%!'; if it is not, the file probably isn't PostScript.)
%%BoundingBox: llx lly urx ury
Or, if you don't want to modify the file, you can simply write these numbers down in a convenient place and give them in your TeX document when you import the graphic, as described in the next section.
If the document does not have such a bounding box, or if the bounding box is given at the end of the document, or the bounding box is wrong, please complain to the authors of the software package that generated the file.