Knowing when to work in black and white can take time during during the post production or even while about to take the shot. I always shoot RAW and occasionally shoot black and white straight from the camera. Sometimes you can visualize your shot in black and white but most of the time when it comes out black and white doesn't really work. Don't worry. Just because a photo doesn't look good in black and white doesn't mean it looks good in colour.
Even though black and white looks cool/retro and vintage, don't feel you have to convert because it's common.