In printer terms typically a margin is the blank space between the edge of the sheet and the image on the page. (note margins on full-bleed documents are a bit different – see the section Bleeds Explained) Basically our printers (actually most/all laser printers) can’t print to the edge of the paper. Instead there needs to be at approximately 1/4” (0.25”) of white space at the edge of the sheet, which is considered to be the unprintable area also known as the page margin.
Most word processors will have reasonable default margins. (many default to 0.5” or 0.75” which is plenty) It’s best if you setup your margins before creating your file, as adjusting them after the fact can be problematic. You may want to consider the aesthetic implications when choosing your margins. A document with margins that are too narrow can make your document look cluttered and dense. Alternatively a document with wider margins may look artistic, academic or more approachable. These are generalities and highly subject to taste, but it’s worth considering when you setup your file.
Bleed is an important concept to setting up your files correctly for print, though it’s somewhat difficult for people to grasp. Basically, if your file has any colour (other than white) running to the edge of the sheet, that colour needs to extend past the edge by a small amount. (usually 1/8″) This excess colour, called the overbleed, gets cut off when the pieces are trimmed down. This is necessary because cuts are never perfect and there needs to be a bit of wiggle room when doing the cutting.
Suppose you wanted to setup a postcard with full-bleed. (standard size is 4×6″) So you would setup your file to 6.25 x 4.25″, with that outer 1/8″ being the overbleed space. (1/8″ on each side gives you 1/4″ or 0.25″ total) Your file might look something like this:
It’s difficult to spot the overbleed so here’s the same file with a yellow box showing the bleed space: (most programs will have a way of adding guides to your document to show you where the bleed space is located)
Now the card will look like this, after cutting:
Notice how the text ‘2014’ is properly centered in the red box after trimming. Take these little details into account when setting up your file. If you consider bleed from the beginning it will make the design process (and printing production) a whole lot easier.