Here are some key features of the Indian constitution that are relevant to the civil services exam:

• The Preamble, which outlines the basic principles and values of the Indian Constitution.
• Fundamental Rights and Duties, which enshrines the basic fundamental rights of every citizen and the responsibilities that came with it.
• The Directive Principles of State Policy, which outlines the social, economic, and political goals of the state and sets out guidelines for the government to achieve these objectives.
• The federal structure of the Indian Constitution, which separates powers between the Union and the State governments.
• The independence of the Judiciary, which is ensured through the appointment of the judges and their security of tenure.
• The emergency provisions, which outline the circumstances under which the President can proclaim an emergency and the powers that can be exercised during such a period.
• The constitutional provisions related to public services, including appointments, promotions, and disciplinary action against the civil servants.

Civil servants are expected to be well-versed with these features of the Constitution, among others, as they have to work within the framework outlined by the Constitution while discharging their duties.