And if there's one word to describe the tests: ENGLISH.Learn it. Speak it. Master it.
The impression the GED gives me is that they want to make sure you are literate. As long as you understand the questions, and the multiple choice answers, you cannot fail. And even assuming you are uneducated, as long as you've read books and magazines and basically know how to comprehend, you won't have a problem. If you don't, well now is the time to start reading, and maybe seeking a tutor.
If I had to pick out my biggest mistake, it was probably the decision to cram for algebra the night before. Math was actually very easy, and as long as you have a basic understanding of how to look at algebraic equations, you'll pass.
Most of the questions ask you something from a passage you are supposed to read. the answer is usually in the passage, either worded differently, or gives you a kind of impression that will appear in the multiple choice.
But again, i must stress that your competency of English is the most important here. If you don't fully understand teh question or some of the multiple choice answers, you might pick the wrong one. I found the actual GED tests to be less technical than some of the practice tests found online, so that's a good sign. Oh, and unless you really need it, NEVER pay for a GED studying course or something. You are better off asking your son or daughter to tutor you than spend hundreds of dollars on those websites!
Good luck! <3