Ensuring sufficient Dots per Inch (DPI)
An acceptable DPI to be used should be within 150 – 300 DPI, otherwise the printed images might risk being pixelated or blurry.
Care should also be taken when images downloaded off the web are used for the design, as not all images which look nice and sharp on your monitor will be similarly good on your final print product. The images should be viewed on your monitor at 100% scale for a more accurate gauge of the pixelation and acceptablity.