If you plan to take the SAT or the ACT in the fall of 2013 (or even later) it is not too early to work on your critical reading skills. I know that parents and teachers are telling students to read as much as possible and they're right. But don't read just anything. Read books and periodicals that are written at a higher reading level.
Here is a quick way to approximate the reading level of a book or article based on the SMOG index:
First mark off 30 sentences. I generally like to choose 10 sentences at the beginning of the reading, 10 in the middle and 10 near the end. Within those 30 sentences, count all of the words with 3 or more syllables. Take the square-root of that number and add 3. The result is the approximate grade level of the reading material.
The SAT and ACT were designed to measure whether or not you could read at the college level, so you can expect the reading levels for the various passages to be 11th grade or higher. By contrast, popular series like Harry Potter and The Hunger Games are written at a middle school level.
Use this method to find reading material at a good reading level for practice. THEN read as much as possible!