So true about orange/lemon/lime! For limes, I like to pick out the ones that have the thinnest-feeling peel. Those tend to be the juiciest. It also helps to roll it on the counter before cutting to release more juices. Typically, the thinner the citrus peel, the more sweet and juicy I've found them to be.
RE: Is It Ripe? How To Know When To Eat Avocado, Mango, and Papaya, Contributed by @sharingeverybite