Some images in mosaic design books can be very complex, It’s very easy to find images with minimal details which will work well for creating a mosaic masterpiece.
Images should have minimal detail as it needs to be simple because it’s only a map.The details, shading and texture come when you add the tile.
Most importantly, it doesn’t make sense to sketch out details that are smaller than your smallest mosaic tile.
Why buy a generic pattern from a stained glass store when you can find more specific images in a colouring book? Colouring books are a good source for images, the range is extensive e.g. human figures, historical events, animals, vehicles, ships, mythological creatures, famous architecture, etc.
Since you maybe converting a simple image with little detail into a a more complex work of art, it’s necessary to add your own elements of depth, dimension and style as you choose tiles for colour, texture and shading.
Consider using 2 different colours or shades of the same colour instead of only 1 colour to create highlights and shading, giving flats shapes some depth
Use bold outlining, outlines should be clear and dark but not thick as big, thick outlines make images hard to see
Incorporate multiple design elements into one work, such as ornamental bordering, or use multiple designs together to create a central theme
Experiment with tiles or stones with varying texture and unexpected colour
Improvise by modifying the pattern to make it for you