Since the invention of modern photograph black and white representation have played a key role into the evolution of the medium. For sure color reddition have been preferred over time for its own added pictural information that eventually partly if not almost completely submerge the black and white (B&W) image reproduction. But suffise to mention that still today color processing is using multi layers of B&W sensitive areas with added applied color to the get the final result.
I wont argue here the virtues of every way of doing photography because in fact they are all justified by the creativity involved in every different processes experimented by the auteur. My point is the following. With contemporary digital camera there is a big new window opened for the B&W photographs in a way that you can actually previsualize your result on screen before the final picture taking action. And that the most interesting aspect of it. No more imperfect (at the most) polaroid tests on the spot to rely. What you over your back screen or electronic viewfinder or your external screen is the "real" visual output. And the technical advancement give a capital advantage to work your B&W output right on the spot something ever dreamed during the traditional film photography era.
As for many others picture reproduction techniques doing B&W photography have its own requirements and limitations. A beautiful color scene doesn't always be translated in a magnificent B&W picture. Sometimes yes sometimes definitively not. Because in part of the fact that the color palette offer psychological contrast (between the colors) that BW gray scale is not able to reproduce totally or simply not at all. So different gray patches will blend each other and the final results will be dull and the image information will be difficult to decode. So as you can presume contrast is a key point in B&W photography.
As for any photographic processes the exposure (the light levels distribution) is another critical aspect to consider. Because your own eye has a very larger dynamic light perception between the highlight and the lowlight it has been always a challenge to produce image captor that can be able to mimic human eye perception. Today our recent image sensor have revolutionized that frontier limitation at a point never dreamed a few decades ago. But still the exposure factor is another key to faithfully master in order to get the full palette of gray tonal you need. On the opposite side you can always redirect you exposure setting to discriminate voluntary part of the gray scale you don't want to register as for example in creating silhouette subjects.
Toning voluntary or not B&W photograph is not a new feature in photography. In the past during the film photography era many paper supports were generating different white tonal renditions from cool to warm as for paper chemical developers that were able to "tint" the silver oxide of the black and gray areas of the picture. Those possibilities have been incorporated in the inboard camera image processors or/and the post processing image applications. It is up to you to decide to register an already (tone) altered image or to wait et the post processing stage of it.
The expression of your main living subject will create a major impact to the first perception of the image because as human we will be attracted especially in B&W by the "face" of the subject. So interaction between the photographer and its model or subject is basically what we apprehend at first. Eyes, mouth and facial expression may be the most difficult photographic aspects to master a spontaneous or not portrait.
(Partial B&W photography and special effects)
Another interest optional feature present in some digital photographic camera is the possibility to remove the entire color palette in profit of only one selected. In that way we create a kind of B&W picture with added color. These studies can be interesting if you carefully compose your image and most important don't forget to still focus on the impact and story of the subject. An array of different "special" and easy photographic effects is now available in digital photography. The danger is that you can distract your auditoire from the main subject as many people can simply skip it.
Finally I cannot emphasizes more the importance to explore the medium. Your (documented) research will help you to raffine your quest of a better picture that will suit your own visual expression. Because at the end B&W photography is just another way to communicate your perception of your living surrounding.
