I guess when you start out with Photoshop, there are many techniques, tools principals and ways you can go. A good start would be to learn about channels and how they are different in each image depending on color and tone. They are a very powerful thing and can be used in many ways.
A recent B&W conversion technique I picked up on is to use a combination of the 3 channels to create a B&W image. Assuming you just have a background image to start with in Photoshop, create a "Channel Mixer" Layer, and select the preset "Black & White with Red Filter", accept, then create another channel mixer layer and select the preset "Black & White with Green Filter". Once you have accepted this layer, go to the little arrow menu at the top left of the layers palette and select "Blending Options" and under "Knockout" choose "Deep". Create a final channel mixer layer with the preset "Black & White with Blue Filter" and again change its knockout to "Deep". http://img165.imageshack.us/img165/297/picture1zb9.jpg
Now you will have a pretty interesting looking B&W image depending on the weight of color in your image. From here its a matter of either creating masks so that only a part of each channel shows in the image, or using the "Blend If" sliders to adjust each layer to create a final B&W. I you want to bring color back into this image, duplicate your original color background image, then bring this to the top of the channel mixer layers and change its blending mode to "Color" then adjust or mask to taste. http://img165.imageshack.us/img165/690/picture2jo2.jpg
It may not be the most simple way to convert to B&W, neither is it a good introduction to channels, but have a play around with the different layers to understand what is contained within each channel and it will help you to understand and get more use out of the channels.