A leaf, or a piece of wood ,the grain of a wall, or even a flower can all make wonderful black and white images even if the color is pleasing - it’s the texture that can be important.
The second thing I look for is texture. Images with a lot of texture will often look good in black and white. A leaf, or a piece of wood ,the grain of a wall, or even a flower can all make wonderful black and white images even if the color is pleasing - it’s the texture that can be important. The photo below looks equally good in black and white as it does in color, due to the texture of the plant.