Your Aadhaar number which is a part UIDAI's (Unique Identification Authority of India) vision to create a digital authentication platform, may not be as secret as your ATM pin, but it’s not to be shared in leaflets or in social media. Keep it as secret as possible. Don’t leave your Aadhar card’s photocopy with strangers. Avoid using your Aadhar number on a website not secured with SSL. Never share your Aadhar related OTP with anybody and keep your Aadhaar registered phone number safe.
Link your Aadhaar to a service only if you absolutely have to. Supreme Court of India clarified the services where you need to link your Aadhaar and where not. You don’t have to submit your Aadhar in bank or e-wallet, to buy a SIM card, during school admission, to appear in CBSE, NEET, and UGC examinations. Private companies can't ask for Aadhar number.
Lock your biometric (iris and fingerprint) data related to your Aadhaar. You can do so by visiting the UIDAI (https://uidai.gov.in/) website and can unlock temporarily whenever necessary. Keeping your biometric data locked decreases the chance of its potential misuse.