Deciding what to B&W?

Just wondering what about a photo makes people think "that would be great in B&W"

Im thinking of doing some B&W but i cant decide what will look good without actually going through the conversion process only to find it looks poor.

Any guidance?

I really don't like b&w much so I only try it if a picture looks ugly in color. And most of the time it doesn't work.
Very helpful I know.

I would usually convert to BW pictures with great details and/or high contrast. Any picture where the main interest is into the details rather than the colors.

Old subjects are my favorite. Old car, boat, building, etc. They always look good in BW.

When converting your pictures to BW, don't just desaturate. Else, pictures will look flat and without interest. I like to use Infra Red filters, add a sepia or slightly bronish tone, adjust levels to increase contrast and add a bit of film grain.

Here's a couple of pictures I recently converted to BW using the previously described technique:

It can also be used as a "get out of jail" card for when the shot just doesn't work in colour (like when I get focus wrong). Sometimes a half decent BW conversion can help out.

Example:

Nearly everything looks better in B/W. Unless color is part of the subject matter, I ditch it... or if it is for more general consumption as people expect family type photos in color.

Sticking with the old boat theme, evidently...

Almost anything; given the fact that for decades most photographers did not have a choice. As noted, scenes with heavy contrast, but also subjects that have subtle tonal gradation, such as a flower. Consequently, shooting on bright days or overcast have their separate but equally effective advantages. Subjects that emphasize shapes, lines, and patterns also standout.

Foggy landscapes, scenes with a lot of contrasty texture, any image really - can be done in B&W. If color doesn't lend anything to an image, try B&W. Try out some random images and see how it works out with those as well. Look at examples of B&W out there and see what others are using it for.