Keep in mind the minimum requirements for remaining in good academic standing, and contact an advisor if you have concerns about your academic performance.
To remain in good academic standing, you must:
Some students have additional requirements and restrictions that are not related to academic standing; for example, international students, NCAA athletes, and students on outside fellowships usually cannot go below 12 units in a quarter. If you think you might earn fewer than 12 units, be sure to consult a UAR advisor to discuss your individual case.
Be aware of the difference between "enrolling" in units and "earning" units. All full-time students must enroll in at least 12 units at the beginning of every quarter. At the end of the quarter, when your transcript shows a passing grade for each course, then you have earned the units. You can earn units with a D- or a CR (Credit) grade. NC (No Credit) and NP (No Pass) are failing grades that do not earn units. Depending on your individual situation, there may be different rules about enrolling and earning units, so be sure to consult advisors.
You can read more about academic standing in the Stanford Bulletin. Financial Aid also has separate rules for Satisfactory Academic Progress that students on financial aid should understand.