Here is a great video from Tropica showing suggestions on how to plant many common plants:
http://www.youtube.com/watch?v=44cDbR2YvK4 (http://www.youtube.com/watch?v=44cDbR2YvK4)
and here is an example video showing how to set up a tank, choose where to place your plants and suggestions on how to trim them plus a summary at the end of the tank's parameters.
http://www.youtube.com/watch?v=Stj8dHrau8E (http://www.youtube.com/watch?v=Stj8dHrau8E)
I wish I could find a pair of those scissors...