As I’ve discussed before, the point of skimming is not simply to read everything fast, but rather to read many things fast in order to identify the handful of places you need to slowly.
While this is generally true for the ACT, there are also some quirks particular to the Reading Comprehension section that make it necessary to approach skimming a bit differently.
1) Initial read-through
One of the particular challenges that ACT passages pose is that they can either focus primarily on a single argument and its supporting and/or contradicting evidence, or on a collection of facts and details that revolve around a particular topic. In the case of the former, you need to focus on the key places in the argument, the places where supporting and/or contradicting information is introduced.
These key places may only occur every other paragraph or even every third paragraph, but if you focus on topic sentences and keep an eye out for transitions such as therefore and for example, and punctuation such as dashes and colons (which signal explanations) you should be able to pick them out pretty easily. In case of the latter (especially Prose Fiction), you do actually need to read everything quickly in order to get a general impression of what’s going on — there’s just no other way to do it. As you skim, however, circle major transitions, explanations, and words like important to help you when you:
2) Go back to the passage in order to answer specific questions
Since the ACT does not usually give line numbers, Reading Comprehension can feel like some sort of twisted scavenger hunt. The trick is to identify one or two key words in the question and look only for them. If a question asks about the architectural significance of Frank Gehry’s Stata Center, for (real) example, look only for the words Stata Center and ignore everything else. If you have no idea where those words could possibly be, don’t just start reading random bits of the passage — chances are you’ll just get lost and miss important information when it does appear. Instead, focus on reading topic sentences to figure out which paragraph is most likely to contain those words.
As your eye moves down the page, draw your index finger along with it
Establishing a physical connection with the passage helps to focus you and makes it easier to spot the words you’re looking for.
Then, when you’ve found them, read the full sentences in which they appear, thoroughly, from beginning to end, and without skipping over anything. If you have to, put your finger on the page in order to make sure that you don’t miss a single word. Pay particular attention to any major transitions you’ve circled in or near those sentences because there’s a good chance the necessary information will be located near them. If you can’t answer the question from the information in that sentence, read the sentence before AND the sentence after it. There’s a good chance you’ll find what you’re looking for.