A surprising share of print jobs come back with a query before they go on press. Almost all of those queries are about the same handful of file details, and all of them are cheap to fix before submission.
Start from the printer's specification
Every printer publishes, or will tell you, five numbers: trim size, bleed, safe margin, colour mode and minimum resolution. Design to those numbers rather than resizing artwork afterwards. If you change the size at the end, type sizes and image crops that were tuned for the original format will be wrong even if nothing looks obviously broken.
Outline the fonts, or send them
Either convert text to outlines in the final PDF, or supply the exact font files with the licence that covers commercial printing. Substituted fonts are the single most common reason a proof looks different from the design. Outlining is the safer default for a one-off print job, provided you keep an editable master.
Set colour the boring way
Use CMYK for process printing and specify Pantone references only where you actually need a spot colour. Deep blacks need building deliberately: a single 100 percent black plate looks grey on press. Rich black recipes belong in the handover notes so the next person does not have to guess.
Check images at final size
Resolution is measured at the placed size, not the file size. An image that is fine on screen can be far too small once it fills an A4 page. Check the effective resolution of every image in the document, and never enlarge a placed image to fix a layout.
Write a one-page handover
Finish with a short note for the printer: trim size, bleed, stock, finish, colour references, and which file is the final one. It takes ten minutes and removes almost every question that would otherwise arrive after submission. Keep the same note with your source files, so the next print run starts from facts rather than archaeology.