The number one problem we see is putting critical elements too close to the edge of the templates which results in images and designs getting cut into. So, keep in mind the slight wander inherent in printing on automated equipment and allow 1/8 to 1/4 inch space around the edges. Turn on the grid in the Design Tools in Lenzart ROES and set the grid size to an appropriate value to give you a guide to stay in the clear.
If using an image as a background, be sure to make that background image light enough, or it will compete with your primary images. Remember you are designing on a backlit screen and what you are seeing will actually print darker. Setting the Opacity tool in the Design Tools to 50% usually works for most images.
Strokes are a fabulous design tool, but be careful to use them to enhance, not take over. Keep them thin and use a nicely co-ordinating color. In the Design Tools, we like to set the stroke width between .015 and .025 (depending on the size of the piece), and use the dropper tool to pick up a color within the design.
The same goes for drop shadows. Keep them subtle, not big and dark so that they take over the design.