I really like the LAB method of B/W conversions, as it adds a slightly dreamy finish to the final outcome and doesn't need too much playing around (for example if you use the Channel Mixer method which needs a bit of tweaking).
If you want to try, the Photoshop method is as follows;
-Change the image Mode to LAB (as opposed to RGB).
-Go to the Channels, and you should see 'Luminance, A, and B' channels.
-Right click the A channel and delete it
-Do the same for the B channel
-Change the image to Greyscale
-And finally change back to RGB
You can now tweak the levels and curves (if you have those plug-ins) to get the black and white points spot on.