You’ve read the Handbook. Now, read it one more time with Understanding Rubric Level Progressions (©SCALE, 2014) alongside.
This is important, as the Understanding Rubric Level Progressions (©SCALE, 2014) document explains in detail what is required to earn a score of “3.” Essentially it interprets the rubrics for you.
It’s important, however, to not just gloss over these explanations once or twice. Read them BEFORE you plan, BEFORE you teach and BEFORE you assess your students.
If you know what is expected, you are far more likely to do it.