First: security

  1. Enable two-step verification with a recovery email;
  2. Hide your phone number and last seen;
  3. Set a local passcode or biometrics;
  4. Review the device list regularly;
  5. Use secret chats for sensitive talks.

Next: efficiency

  1. Set a username so people can find you;
  2. Use folders to group chats;
  3. Treat Saved Messages as a drive and draft box;
  4. Pin important messages;
  5. Learn global search and hashtags.

Finally: comfort

  1. Configure auto-download per network;
  2. Set quiet hours and custom sounds;
  3. Switch to dark mode;
  4. Clear cache and set media retention;
  5. End web sessions after using shared computers.