The replies here have been interesting.
In the interest of full disclosure, the example in my reply is for installation only. Truck measurements and photos have already been taken, and a scale layout has been prepared. I take "straight-on" photos using a long lens (to minimize parallax distortion), run the images through perspective correction using Photoshop, the spend some time getting an acceptable layout. Once the layout is approved and the graphics are prepared I schedule the installation. The design costs and materials costs are marked up and added to the installation cost. Design and layout often take more time than the actual installation.
With the layout in hand, I tape the graphics up on the truck, then correct positioning. I usually try to have all the graphics "lock up" (all oriented on the same horizontal axis). The eye is drawn to the graphics, and having them all on different horizontal axis looks clumsy. The basis horizontal axis is determined by the lines of the truck, and everything else goes off that (some adjustments may have to be made, such as lines of text near the top of a pickup bed, where the text will look crooked if they don't line up with that strong horizontal). The eye is the final arbiter. Once I'm satisfied, I make small marks on the truck so I can remove the taped up graphics and register the graphics to the marks when applying. By the time I get around to applying the graphics, I don't have to think about where they go, and I can concentrate on a clean application.
Labor rates are determined by marking up the "burdened" cost of labor (actual pay plus payroll tax, workers comp, and general liability insurance). In general, that cost is usually around 30% of the ticket, materials 30%, overhead 20%, leaving a 20% net profit. The $85/hr rate I used in my example works for us in our lower cost of living market. If you live in a metro area you will likely need to charge more. That is a shop rate, our installers have a higher rate (their burdened cost is considerably more).