If you design your own artwork save the time it takes to bring it up to print ready state simply by keeping these following important points in mind.
Proper Resolution
Irrespective of the Graphic Design tool you use, be sure that the standard Dots per Inch of 72 is not sufficient for printing, graphics at that many dots per inch are good for a pixel driven display like an LCD screen, but for printing on paper, much larger and denser images are needed. So before you start working on your artwork, be sure that the DPI is set to 300.
Bleed, Trim and Safety Lines
Print Size and some extra space all across the edges is important,. Create a graphic that is slightly larger than the intended output, in case of printed paper cups, the template to layout your artwork on is not a flat or square or a rectangular design area like shown here, but the bleeds are still very important there, it ensures that while forming the cup no important part of your design is lost inside a fold or gets cut off.
Bleed: When your artwork is printed, it is printed on paper and then trimmed to fit the specific size, so if you need a business card of size 2 x 3.5″ and you design the exact size, at the printers tool, when they cut your stack of cards to size after printing them, your artwork might fall a millimeter short of filling the full size, thus leaving ugly white borders around the artwork.
Thus the practice is to plan a design size that is 1/8″ extra at all edges. Which means for the above business card, your document should be 2.25 x 3.75″ when you are designing the piece. This leaves some space for the printer to work with, without destroying your work.
Trim Lines: To keep yourself conscious about the bleed area, draw the trim-lines as reference in a layer. You’ll know this is where the document will be cut, so you won’t put important objects beyond this line.
Safety Lines: Additional 1/8″, this ensures that if its a book, a thick book, even then content doesn’t get hidden into the folds of the binding.
RGB, CMYK, 100K Black & Rich Black
CMYK: This is for those who mostly design for the web, and are comfortable in using RGB color schemes for all the vibrant designs you have been creating. Printers do not use Red,Green and Blue inks, they instead use Cyan, Magenta, Yellow and Black inks, and to be true, these colors do not always translate well from RGB. So do not forget to use a CMYK color pallete.
Special mention should be given to the color Black, if the black ink that the printers use, is used to print a large black area, for examplea black background, it looks gray, so for large areas use Rich Black, with the same proprtions of the colors are shown.
For texts below 36pt, borders and lines use the 100k Black, that is, as you can obviously see, only the black ink. For small texts and lines, using only the black ink is safer too.