Understand the Basics
With most print jobs, you should have specifications to adhere to. These specs work for preparing advertisements, brochures, business cards, and other printed mediums.
CYMK vs RGB
A lot of the colors you create in RGB mode are not achievable using standard four-color process printing. It is always best to create your document from the start in CMYK color mode to ensure that you have a better idea of how your colors are going to print.
Some exceptions are tradeshow signs or large format prints, but the best way to know for sure is to check with the printer.
Four over Four (or 4/4)
If you’re printing a flyer, you might be printing 4/4, which essentially means you are printing four color on the front and four color on the back. If nothing’s on the back, then it would be 4/0.
For postcards, you might print 4/1: four color on the front and 1 spot color on the back.
For business cards, you might print 2/2: 2 spot colors on the front and back.
Here is a diagram of a typical document for print designs.
Trim Line: This is the finished size of the piece.
Live Area: The area that is considered safe to keep any important information within. For example, if an ad’s trim size is 8.25 in × 10.25 in, the live area might be 7.75 in × 9.75 in. This takes into consideration the binding if the ad is placed on the left or right of a spread and you don’t want copy to be unreadable if it is too close to the spine.
Bleed Area: The more bleed you can offer, the better.The minimum bleed you need for a printed piece is 0.125 in (1/8 in) but some specs require more than that. So if you are working with an image in Photoshop and you’re placing it in InDesign for print preparation, keep in mind the area you might need to use for the bleed.
Crop Marks: Indicates where to cut the paper.
Read more at https://www.webfx.com/blog/web-design/a-guide-to-preparing-files-for-print/