http://www.acrylicosvallejo.com/
Go to this link, select "Model color" from the drop down menu and scroll tot he bottom of the page for a downlodable and printable tutorial.
Yes, 50/50 will give you a very thin layer. It's supposed to. You need to lay several coats on to build up the color. For large areas, I use a #4 flat shader by Lowe-Cornell and just a bity of paint at a time. You may need 3-4 water thin coats to get the full effect.
The theme song for Vallejo (and Andrea) is "shake, shake, shake; shake, shake, shake, shake your bottle, shake your bottle."
I assume you've primed the model first?