It appears I start many tips the same way, so in keeping some consistency... Back in the days of film...
Black and white processing for digital images has come a long way from the horrible B&W converters of old or just dragging all the saturation away in a colour image to make a black and white one.
We now have superior post processing tools designed specifically for the creation of black and white images. The two that I am inclined to recommend are Nik Softwares Silver Efex Pro 2 and OnOne Softwares Perfect B&W.
Both products offer a number of really well done presets that could be the end or the beginning of your black and white creations. The primary thoughts that go into black and white digital processing are a) maximizing the dynamic range of the exposure and b) getting the contrast to the right levels to facilitate story creation. By removing colour, the viewer must become more engaged in the story making process and so our artistic intent has more power, given that the pretty colours are stripped away. Think of the multiple fall leaves images or sunsets you have seen and think of what story they initiate if devoid of colour.
One of the lesser used functions in black and white digital processing is the use of coloured filters. When we shot B&W film, we carried an assortment of coloured filters that by filtering out their own colour, would change the look of the black and white image, sometimes substantially, to help create the storyboard. With digital processing you dont need to carry sleeves of filters for b&w anymore although you can if you wish. Its just a lot easier to do this in post. Lets take a look at the effects of some of these filters. Note that most of the these filters can be applied in post processing, but two of them, the Neutral Density and the Polarizer are only effective when used at time of Image Capture.
When I started shooting film, one of my mentors at this time, an awesome fellow by name of Jim Brotchie, told me to go out and get a Yellow filter and put it on the lens ALL THE TIME when shooting b&w. He convinced me to set an adjustment on my handheld meter (my camera at the time had no internal meter) to compensate for the light loss when shooting with the (Y2) filter. Yellow filters reduce the yellow and so enhance blues and improve contrast overall. You do have to watch that they dont increase the visibility of human blemishes too much but the effect is nearly always an improvement. If you dont know where to start when processing b&w images, try adding a yellow filter first.
Go figure that an orange filter is like a yellow filter only stronger. The same guidelines apply, but you have to be more careful with reddish subject matter going lighter. This filter is very useful for b&w images of fall colours since it lightens oranges and reds while darkening greens and blues. Some really stunning images of Chicago blues musicians with very dark chocolate skin had beautiful contrast and texture appear, when an orange filter was applied.
Red filters were most commonly used with the old infrared films, but work very well on some landscapes as they deepen the blue of skies and make reds nearly white so you can get very interesting juxtapositions with red leaves and blue skies. Whites, greys and blacks transit mostly unchanged so you can really make outdoor images pop. Red filters for people produce a very pale skin on caucasian people and whiten reddish areas like lips and blemishes. For the most part a red filter is not optimal for human beings.
A light blue filter makes blues light and darkens reds. So not particularly optimal for landscape work but wonderful to soften blemishes and to create contrast between skin and lips on light skinned people. Pretty much the go to filter for b&w images of women. Use caution because very bright blue eyes can take on a possessed look.
Not really useful as they tend to block up contrast heavily and darken most colours. Try as an experiment but not a filter you are going to use a lot.
Greens will lighten foliage and may increase contrast in clouds. Some people like the effect on skin in portraits. Again something to experiment with, but certainly not a go-to filter for black and white.
We know what ND filters do. They reduce the light transmitted to the sensor. This allows us to slow shutter speeds or increase the aperture size for creative effect. These filters should be in every photographer's kit and are one of the two that you really need to be using at time of capture.
The Polarizer is most often considered to deepen blue skies or to remove reflections in colour photography. It adds the same value to a B&W image so if the plan is to go make images that will be B&W processed, use the Polarizer for the same reasons you would for colour. The Polarizer must be a real filter and is used at time of capture. Polarizer effects in post processing or for the most part, lousy.