Preparation for the Praxis reading test comes down to advice more than hard-and-fast rules. There simply aren't rules about understanding a passage that you're asked to read. But you can prepare for any test, no matter what it concerns. And in a way, it can be a relief that the Praxis reading test doesn't involve having to accumulate outside knowledge beforehand.
Perhaps the key is simply to forget that you're even taking a test. After all, you're reading this right now, and you don't have any trouble understanding — and the paragraphs about which you're asked questions on the Praxis reading test are mostly about the same length as these paragraphs right here. So a big part of success is just not to get psyched out and assume that the right answers must involve something counterintuitive or tricky just because you're taking a test.
The golden rule of any reading-comprehension test is Occam's Razor, the famous philosophical principle that states, "The simplest explanation is probably the true one." That doesn't necessarily mean that the right answer is always the easiest statement to understand, but rather that you should train yourself to keep your eyes peeled for the least complex statement that isn't contradicted by the passage.
The more detail an answer choice contains, the more possible ways there are for the statement to be false. That's why reading-comprehension tests are often difficult for students with poor test-taking confidence: They assume that the right answer is complicated or over their heads, so they're frequently fooled by overly detailed wrong answers without paying any mind to the simpler right answer that was right under their noses all along.
There's no such thing as a "more right" answer. Every question in the Praxis reading section has five answer choices, of which one is right and four are wrong, period. A "right" answer simply means an answer that isn't wrong, and that's all it means. The choice that answers the question and doesn't contain any information that is falsified by the passage is the correct one, even if it's not that detailed, specific, or interesting. Going out on a limb after a more interesting answer is exactly how you get fooled into picking one of the wrong choices.
The way to ace the Praxis reading portion isn't to look out for right answers — it's to look out for wrong answers and eliminate them until only one choice remains. When you say an answer is right, you're necessarily saying that the other four are wrong — so if one of the other four isn't wrong, you should pick that one instead.