i find it useful to simply make small dots where they should be and then use the smudge tool with a regular rounded brush the same size as the dot and smudge in the direction the whiskers should go. Play around with the settings for the tool.
You could also use the brush tool to simply make strokes where the whiskers should be. In the options menue for the brushes, play with the settings so your brush will fade out.
When using a mouse it is sometimes hard to stroke tthe way you would with a pencil. So you could also use the pen/path tool to create paths where you want the whiskers. then, again, set your brushes as you like (just like in method 2) and "stroke path with brush" This may save some time over method 2.
Hope this was helpful.