I did a little smartphone photography the other day.
The original file was in colour. I imported it into Lightroom, converted it to black and white, and cropped it to a more agreeable shape. I then spent a bit of time working on the tones, ensuring that the alliums stood out against the background. I used mainly the basic sliders in the develop module, along with some neutral density filters to even out the tones. This was the biggest challenge because the original has some subtle but visible shadows and I wanted to neutralise them somewhat. A useful tip is to squint to see if the tone works. You can also try standing back from the screen to see if anything looks uneven.
I've included the original shot below so that you can get a sense of the processing. It's wonderful to have such smartphone technology. It was one of those occasions where I was without a camera, on my way to an appointment, and just happened to spot the wall. Having my mobile with me gave me the option to exercise my creativity and see if my visualisation of the black and white image would work.