To make your blacks a lot richer, add a little cyan, magenta and yellow to the mix and you will get a much better result. Each printer has their favourite breakdown of the four process colours. At Caxton we have found that 100% black and 20% of cyan, magenta and yellow works great! IMPORTANT NOTE: Keep text, especially small fonts at 100% black.
Don't get confused with the "registration" black breakdown that you will find in many software applications. registration is 100% of all FOUR colours which is only used for the registration marks and crop marks and should not be used for any of your black objects or text. One Hundred percent of all four colours will make the overall ink coverage way too much.