Why should I flatten my Photoshop file instead of sending it with many layers?

When a Photoshop file has flattened layers it reduces the chance of a problem with the file to almost zero. When layers are present and not flattened, fonts and other aspects to the file may get lost or not embedded.

Why do I need to convert all my fonts to outlines or curves when I work in art programs such as Illustrator?

Certain programs allow you to 'Convert to Outlines', also known as paths or curves. By converting text to this format, it rids of the need for fonts to be sent along with your file, in addition to eliminating a possibly delay time with your job due to missing fonts.

What is the difference between Spot Colors (Pantone/PMS Colors) and 4-Color Process?

The Pantone Matching System, abbreviated PMS, is a color system used to match ink colors. By using PMS colors, designers, vendors, and clients can use the same PMS # and not have to worry about having an ink color look different.

Why should I save my images as high-resolution JPG's or TIF's (300 DPI+)?

Without saving in a high-resolution format, pixels and details in the image may get lost or may not come out as expected when printed. Usually any images with a resolution less than 300 DPI (Dots Per Inch) appear pixellated or "blocky" when printed.