The first time I tried sprouting an avocado, I got a tree that lived in a pot for about 4 years. Ever since then I have not been able to get a pit to sprout.
I have 5 pits that someone saved for me last year and I'm going to give them a try. However they are completely dried out. They now look like little black walnuts once I removed the brown papery covering.
Are these worth even trying to sprout, or once they've dried out is there no hope?
If they are all dried out then they are dead. Avocado pits need to be planted pretty quickly after being removed from their fruit.
On your first success, how did you start the pit? The method I've had the most luck with was suspending the fresh and thoroughly washed pit over a glass of water using toothpicks stuck into the seed in several spots, with the bottom of the pit kept just barely under the water and the top (more pointed part) kept out of the water and dry. Especially if you can find a slightly overripe avocado as a subject, this generally will yield a sprout in just a few weeks. After it has a decent root system, you can move it to a regular pot with a light but moist potting soil.
If you are not familiar with the toothpick method, here are some pictures that illustrate it.
