Here at StressFreePrint we ask for all artwork to be supplied with a 3mm bleed. This is to avoid any essential elements of your artwork being removed and avoid any unsightly white borders around your finished product.
Some programs, like Adobe InDesign, allow you to add bleed through the document settings. You then just need to place your content with any background colours, patterns or images you wish to extend to the edge of your print, overlapping the trim area and extending to the bleed line shown in the software. You can then save as a high quality PDF using the "use document bleed settings" option.
For other programs, such as Microsoft publisher or Photoshop, you may need to create your document 6mm larger (for example 303mm x 216mm for an A4 size print) and keep all your text and logos at least 6mm in from the edge of your page.
Whilst bleed is important to avoid white edges on your artwork, to avoid items like logos and text being trimmed away please be sure ito include the just as important safe area on your artwork.