Most players want to improve their serves, but many of them don’t know where to start.  Here is what I would recommend…
 
#1 Decide what serves best match your game
 
#2 Find a top player who serves those exact serves
Here are some sample videos…
http://www.youtube.com/watch?v=wbrmRarOysk&feature=related
http://www.youtube.com/watch?v=miIX2BxpQ4E