Talking about the format first, because many times you don’t want to work on the graphics before you have a clear vision and set format of your game. You want to make sure you have the sizes of your game pieces worked out, as well as the cards tokens and all the rest. That way when you start working on your graphics you will have a better understanding of the sizes of font and text you want to work with, as well as the size of art pictures, and none the less you can implement the bleed, the bleed is the graphic part of your game that will have to be drawn outside the borders of your cards and pieces in order to make sure the cut is precise and gets your creation in just right.
The art work is the main interface that will reveal your game to the world, and even though art will not make or break your engine, and the fun of your game is dependent on many other technical factors, it will hold a great deal as far as getting your clients in the future pick up your game from the shelf and go pay for it at the cashier. Artwork will also be the main parameter that will set the mood and atmosphere in which the game is taking place, so give the art an honorable space of respect.