I run digital presses every day, and I can tell you that most print problems are not press problems. They are file problems. The design was fine. The file was not ready.
Here is the checklist I run before any job goes out. It takes ten minutes and it has saved clients a lot of money.
1. Bleed and safe margin
Add 3mm bleed on every edge (0.125 inch if you work in inches). Anything that touches the edge of the page must extend into that bleed. Then keep all important text at least 3mm inside the trim line. Cutting machines drift by a millimetre or two. If your text sits on the trim line, some copies will lose it.
2. Colour mode
Convert to CMYK before you send. If you send RGB, the RIP will convert it for you, and you will not like the choice it makes. Bright blues turn purple. Bright greens go flat. Convert it yourself so you can see the shift and correct it.
Also: pure black text should be 100% K only, not a rich black mix. Rich black on small type gives you registration fringing.
3. Resolution
300 DPI at final print size. Not 300 DPI at the size the image happens to be — at the size it will actually print. A 300 DPI image scaled up to 200% is a 150 DPI image. For large banners you can go lower, around 120 to 150 DPI, because nobody reads a roll-up banner from 30cm away.
4. Fonts
Outline your text or embed the fonts. Every print shop has a story about a job that came back in Arial because the font was missing. Outlining is safest, but keep an editable copy for yourself before you do it.
5. Overprint and spot colours
Check your overprint settings. Unintentional overprint on white objects makes them disappear. And if you are not printing spot colours, make sure there are no leftover spot swatches in the file.
6. Export properly
PDF/X-1a or PDF/X-4 for most jobs. Include bleed and crop marks. Flatten transparency if the shop asks for it.
One last thing
Ask the printer for their spec sheet before you start. Every shop is slightly different. Five minutes of asking beats a reprint.
If you want your artwork checked before it goes out, or you need the whole thing designed and prepared properly, you can reach me — I am Md Alamin Ashif, and print production is the part of this job I actually enjoy.