I need to send a design to be published in a newspaper. I assume this must be restricted to several factors, size, color space, halftoning, etc.
Are there any specific requirements?
There are a few (very general) considerations when sending files to be printed in newspapers. The main areas you should focus your attention on are the ones you already do when designing any print piece (font size, for example) and in particular, color, because of the way newspapers are printed.
If your ad / design is running without color then all artwork and colors should be black and shades of gray. If your ad is running with color then all artwork and colors should be black and shades of gray and utilize the CMYK color model.
Ink is applied one plate at a time with black being the last. White text over a CMYK background can end up looking ‘fuzzy’ due to misalignment of the web of paper as it prints through the press.
Contrast is paramount. Maintain a 20% difference in shades of black for reproduction. If your advertisement is color you can consider creating a temporary creative version that converts all colors to grayscale. Then check for that 20% difference.
Transparencies do not reproduce well. Flatten your artwork to reduce or eliminate as much transparency as possible.
Avoid type less than 6 points in size. Fonts composed of very thin strokes may not reproduce well either.
Check the vertical and horizontal measurements of your advertisement before sending it in. Measurements are generally expressed in the fashion of ‘number of columns’ by the inches decimal depth of the advertisement.
The only thing I'd add to Yisela's excellent answer is this: explore the newspaper's website (or call them up and ask to speak to the production manager) and find their specs. Each production line is different -- the particular press, its age, the staff who run it, the paper they use, the prepress and editorial software they use, all make a difference. If you do this, you'll be something of a hero to the publication's production people, because very few designers ever take the trouble. And it might save you and the client from an unpleasant surprise.
If possible, get a .joboptions file (which contains their preferred Acrobat Distiller/PDF output preset) and which color profile they prefer. Even for a black-only job, it makes a difference if they need you to output for a dot-gain of 10%, 15% or 20%.
Be sure you know what their requirements for ink limit are.
You can use a soft proof in InDesign or Illustrator based off the color profile they specify, to get a reasonably good idea of how the finished result will look.
In general, don't fret the color of the substrate. While you'd think that pink paper would require you to dial back the reds a bit, your ad would be surrounded by pink, which might require you to dial up the reds a bit to achieve the same perceived color.
Color is a complicated subject, and achieving absolute color accuracy is all but impossible in that workflow without going to extreme lengths that aren't likely to be within your reach. What you can do at design time is change the "Paper" color in InDesign, if that's what you use, to something that approximates the paper color of the publication you're sending to. That won't change your output ("Paper" will still be transparent in the PDF), but it will give you a better feel for what you're designing.
The info Yisela and Alan provided above is excellent, and on the mark. A couple other things to keep in mind.
Photos used in newspaper are best built at 200dpi. Images for most other high quality publications, packaging, etc, are typically built at 300dpi. This is due to the dot gain Alan referred to.
Reversed/knocked out text (i.e., white text on a black/colored background) is not advisable under 12pt type, especially when using a serif font.