What is the best way to make pictures black and white?

Go to the B&W panel in Develop’s right hand side and activate the targeted adjustment tool. That’s the little button at the top left of the B&W panel. It makes the cursor look like a pair of arrows which you can drag on the image itself. As you drag, LR moves the sliders for you.

Drag up and you lighten how that area appears in greyscale, downward darkens it. The important thing about this method is that it means you keep your eye on the picture’s changing appearance all the time you are adjusting it. That makes it much better than guessing which slider you should drag, and continually moving your eyes between the picture and the sliders. You inevitably produce a better black and white version, and faster too.