When I use liquid shampoo I've started out bent over so all my locks fall forwards and then put a tiny bit into the roots at the back of my head, then flip over a few locks and put a tiny bit of shampoo in the roots there, and so on and so forth, until the shampoo's in tiny bits all over my roots, then I massage into a good lather that I squeeze into the locks themselves.
When I've had a shampoo that's more viscous I've actually done what you're describing and watered it down into a squeeze bottle before I've done the same thing as above.
I don't go through a lot of shampoo, needless to say.