To familiarize yourself with the format -- short or long, single or paired -- and type of texts -- narrative, poetry, technical, popular or analytical -- you will face, practice reading similar passages. Many tests are in SAT or ACT critical reading format, so if you don't know what you will encounter, use those reading passages for high school level practice, PSAT passages for middle school level and GRE passages for college level.
If long passages are difficult to read and remember, try an abbreviated initial reading: Read the introductory blurb -- if there is one -- the first inch, the first sentence of each paragraph and the last inch of the passage. As you read, underline key points and circle transition words such as "but," "however," "also," "therefore" and "in conclusion." This will help you map the general flow of the passage before you read the entire passage for details.
As you read each paragraph, underlining important points and circling transition words, think about how those words affect the direction and the author's point. Practice summarizing each paragraph by writing a short memo after you read it. When you are finished reading the passage, review your memos and think about how they reflect the organization of the passage: the introduction, the author's points and supporting details.
Be alert to the author's tone, expressed through key words and pointed statements. Notice how the tone supports the thesis. Look for positive or negative descriptive words and literary devices, such as metaphors, questions, exclamations and the use of humor or sarcasm.
In the long term, better reading scores come from reading lots of challenging writing of various types -- fiction, news, poetry, academic writing -- and in a range of fields. Look up words you don't know and keep a vocabulary list. Think about what you read; don't just skim. Discuss your reading with others to gain new perspectives. Although we live in a world of 140-character Tweets, reading is still the foundation of civilization, and along with writing, the most important academic skill you will ever learn.