So yes, consistency is key.
Now everyone will have a different consistency they prefer working with. Some people have just one consistency for everything and some have up to like...i dunno...5. I have 2. Well, I have more than two really...more like 4....but for basic decorating I have 2: Piping and Flood.
An example of cookies made with 3 icing consistencies as opposed to the basic 2
For piping icing you want to make sure that you have it stiff enough to hold it's shape, but not so stiff that it could possible be used as cement.
For flood icing, you will want it to be thin enough that it will smooth down leaving you with a smooth satin surface, but not so thin that it oozes everwhere. I don't use a 10 second rule. Too thin for my liking. I use a 12 to 15 second rule.
Smooth flood icing
Now, I will confess that the secret to perfecting icing consistency is practice. If you look at any of my early cookies you can tell that I wasn't quite there yet. 2 years later, I still don't get it perfect all the time.
So get in that kitchen and start your alchemy! A little drop here, a little drop there. Be patient and experiment and see what your icing will do for you!