Considering the usual test format, simple conceptual questions first and detailed solve-the-problem-and-show-your-work questions last, it isn't a bad idea at all to work tests backwards. The questions worth the most points are almost always the detailed problems. It is also the only part of the test where partial credit is even a possibility. You cannot get partial credit on true/false or multiple guess, and you'd really have to argue the point for partial credit on short answer problems.
Besides, once you work a few detailed problems to warm up, the conceptual short answer questions usually flow a lot more easily. The hardest lesson I had to learn about test taking is that you absolutely must NOT force yourself to go in linear order, start-to-finish. If you do that and you ever get stuck, you're screwed. Not going in straight linear order is very much against my natural personality, but I do much better when I make myself just keep going and come back to problems that I couldn't get the first time once everything else on the test is done.