i think boards like this is your best all round option as peter says. the down side is there s allot of boards offering very bad advice as well as good.
there are some great books from experienced sign writers and the like but not on vinyl. i have found that anything in a book these days is very outdated and basic with regards to vinyl app.
its also back to you need more visuals in seeing how to apply. one of the reasons im trying to steer the site more towards video demos etc, though there is a big learning cuve in that for me too, but i am slowly getting there. books come in ideal is on hints and tips on sign layout, use of colour etc books like the ones paul has suggested from handovers or sign craft mag does that and more. you can be a vinyl guy or a sign writer you still have to learn this sort of thing to make a good sign.