I'm preparing to take the MCAT on May 10th, and I'm convinced that, once you get into the 13-15 range on the verbal (and even the PS and, to a lesser extent, BS), it's primarily luck that determines where you fall in that range. If you get all the questions right, you get a 15. If you miss one, you get a 14, and if you miss two to four, you get a 13. These aren't hard and fast, but it seems pretty consistent. I've often missed just 2 and gotten a 13 on practice tests, and it drives me nuts.
The point, though, is that a fluctuation of 1-2 additional questions wrong or right is likely entirely luck of the draw. So if you're in the range of 13-15, I don't think there's a lot you can do to ensure a 14+. You can practice a lot, though, and that may make a difference.
One generic piece of test-taking advice, especially on verbal-type sections, is to spend more time eliminating wrong answers than looking for right ones. Wrong answers, if you look closely enough, are usually wrong for a very specific reason - often just one word in the answer choice is enough to make it wrong. Right answers, on the other hand, are frequently just "right" enough to avoid being definitely wrong. This makes them harder to spot for what they are. If you practice this technique a lot, you'll get used to the types of things that make those wrong answers wrong, and your verbal score is likely to go up some.