The #1 problem I had in my 15 years in the print industry? Convincing designers not to design problems into their layouts.
The one example I'll give you has to do with understanding the effects of dot gain and last printable dot. Imagine a blend/gradient from a color to white.
On the web, no problem. In print, when the tones of your gradient get to press, two things happen. The halftone dots used to create tones get "squashed" and "fatten up" due to the fact that inks is a liquid, pressed onto paper, causing an increase in density (darkness) of tones. This is called dot gain and can be controlled, but only by sacrificing one end or the other of the range (shadows or highlights.) When those tones get to the lightest end, in the 3-5% dot range, they "drop off."
The combination of these two effects causes and increase in contrast of the entire tonal range, and right where you want it to "drop off" to white of the paper, it hardens and forms a line, ruining your smooth gradient to white.
The solution is to never "fade to white" - always fade to a 3-5% tone, and let that bleed off the paper. Most designers react to this with something like "this is a printing problem, don't ask me to solve your problems for you." It's not. It's a lack of understanding of the printing process. And it's not one we can solve without redoing your artwork.
So my advice is if you want to design for print, you need to understand printing. Some key trouble areas:
- dot gain
- last/first printable dot (works on the other end too; you CANNOT fade to a "full 100% black" in full color printing causing does to "plug" as described above, in reverse.)
- Ink tacking (related to above, if you could fade to a solid black, successive layers and overprints wouldn't stick. Also relates to UCR/GCR below.)
- Trapping (spreading and choking) (spreading one color into another so that a white line doesn't form where two colors adjoin)
- gray component replacement and under color removal, and when to use which (UCR/GCR)
- Special applications of printing colored type (comes into play with trapping)
- When to use overprint, and when not to
- Digital issues: correctly linked images versus "embedded" issues; using DTP-compatible programs; preparing for service provider
- Folding and trimming: I always found it amazing that few designers understand you can't split a page into three equal parts and have it fold properly into a 3 panel brochure. You have to have a short panel. This is true of any folded material.
- Understanding stock sheet print sizes. You might not care, but your client will really care when he gets the estimates for the difference between a bleed and a non-bleed. (understand what a bleed is too . . . )
- Understanding the relationship between stock quality/color, DPI of printing and choosing the best DPI for your print project.
There are more, these are just the big ones. I hope you're gathering one important point: you need to understand the print process. This is where you should start, learn about the industry you're about to dive into. It will save you a lot of frustration.
Print is not a dying art, yet. What is growing less and less of an art is preparing the artwork for it properly.