Thanks!
For a long time, I would just estimate the FOV. You get to the point that you can pre-visualize the composition often peaking with both eyes. The M8 itself has the 24mm frame lines but has a crop factor. Now, I'm really enjoying the M9 with the 24mm (the last one was taken with the M9). I still often shoot without a viewfinder and rely on just estimating. Fortunately, I still have the viewfinder that I got with my Panasonic LX3 and it works like a charm. Not as big and bright as many of the viewfinders but it works just fine. If its been a while, I would take a few test photographs to remind my brain what 24mm looks like (a welcome benefit to digital).
Often, people can visualize the 50mm focal length. If you are careful to also include a bit of your human peripheral vision (both eyes), you can (with practice) pre-visualize 24mm as well. Its about as far wide you can go without having more complexity and distortion.
Its the lens I often use for quick dynamic situations (street photography for example). You can zone focus it fairly easily and it captures enough surroundings to complete the story even while you focus on a subject. Yes... at times, I will also crop appropriately (oh my!) to the finished print.