I've always been a big fan of Black & White photography. Old photographs printed when paper still had real silver has some of the best tones which are just not available with the papers we have today --- especially not with digital. (To see some of the best range in grays check out Ansel Adams.)
But alas, you have to adapt to the times. This means shooting in color and converting to grayscale later. There are various ways to convert to grayscale ... how you do it will depend on the picture and your liking. I'd recommend selecting a picture, doing all the below listed steps and seeing the differences on your own.
NOTE: You can convert to grayscale straight from Camera Raw, below are the methods in Photoshop. ALSO, before your play with the below methods, go to HISTORY OPTIONS and select ALLOW NON-LINEAR HISTORY. This will record all the below actions so you can easily compare differences. Each time you convert go back to the original color image in the HISTORY panel and try the next method.
1. Go to IMAGE in the toolbar. Go to ADJUSTMENTS. Select DESATURATE.
2. Go to IMAGE in the toolbar. Go to MODE. Select GRAYSCALE.
3. Go to IMAGE in the toolbar. Go to ADJUSTMENTS. Select GRADIENT MAP.
----Under this selection a dialog box will open, click on the little down arrow next to the gray box. Select the 3rd option from the left, which is a box that goes from black to white. Click OK.
4. Go to IMAGE in the toolbar. Go to MODE. Select Lab Color.
----Under this selection you'll now need to go to CHANNELS. Here you will see 4 boxes, click on the box that says 'lightness' ---- be sure to click the image and not the little eye. = ) Once you've clicked on 'lightness' and only that box is highlighted, go to IMAGE in the toolbar. Go to MODE. Select GRAYSCALE.
5. Go to IMAGE in the toolbar. Go to ADJUSTMENTS. Select Black & White.
----This will convert to grayscale and will open a dialog box so you can adjust colors. The color adjustments work similar to filters used with a camera. For example if you take away blue your sky will get darker. If you add blue your sky will get lighter. This option is good except there is no way to know when you are loosing information in your image, you'll need to rely on your visual preference.
6. Go to IMAGE in the toolbar. Go to ADJUSTMENTS. Select Channel Mixer.
---- This will open a dialog box. At the very bottom select where it says MONOCHROME. this will convert to grayscale and will allow you to adjust the colors similar to the above option. However, be sure that Red, Green and Blue add up to 100% --- this is the advantage over the above method. Also, if you go to the top of the dialog box and hit the down button you can select presets such as Infared Filter etc.
I'm a big fan of method #6. I used this for the below images and kept most of the color at red. A red filter is great for portrait shots as it evens out the skin and gets rid of blemishes.