What recommendations do you have for mug designs that are front & back print?
Our mug print area is roughly 3" x 3" so it’s generally recommended for art to be in more of a square format rather than rectangular because it will appear larger and it will take up more of the 3" x 3" area.
Many logos are designed in a horizontal orientation which does not take up much room of a 3" x 3" space. For your logo to appear larger and more prominently on mugs it may be beneficial to adjust the design of the logo to more of a square format.
REGARDING FONTS --
More slender fonts (and this also applies to fine/thin decorative lines) can be more difficult to read on the printed mug.
It may be better to use a weightier font for your designs. This is especially true for black mugs.