Bleed is the area that extends past the finished document and it will be cut off the printed document. If you are using background colours or images close to the edges then extend this past the bleed in order to avoid a change of colour at the cut edges. We use 3mm bleeds. Note this applies to all 4 sides of the document, i.e. total extra area is 12mm.
Keep all important text and images at least 4mm from the edge of the finished size.
Prepare your file using CMYK colour mode.
Make sure the resolution of the images and graphics are at least 300dpi.