I usually just add approx 16 Cyan, any where up to 30%Cyan can help, but it will depend on the printers, and the type of project it is for...
Perhaps a little more information on the project would help, such as obviously this is for print, but is it for business cards that will have very small writing on it, and magazine advert - will the text over the black be large and blocky, or will it be small and fine?? How will the project be printed? If it is an advert, will it ever be used in newspaper print?
You could just ask the printers what rich black would work best on their press. I've found sometimes if I use a certain rich black with one it might look different with another (had one come out with a slight blue tint that bugged the hell out of me). If I choose to use rich black now I just throw in 50/50/50/100
A fair bit of my own design is for newspapers THIS IS ONE OF MINE, AND ANOTHER (the Rotty ones do like black for some reason) They both printed 100% correct, considering who printed and the fact it was on the next step up from bog roll, as Steve mentions. Both the above blacks where produced using 20%Cyan and 100% Black with nothing much else.
The one thing you really got to be carefull of is the size and "fine-ness" (if thats even a word) of any text on top of the black, it's not really an issue for digital print, but for litho and ESPECIALLY newspaper print - newspaper print can shift out of register, and if you look at some of the cheaply produced newspapers (usually the freeby local rags) you may see this, especially if it's a friday afternoon print run:icon_rolleyes: .