First: security
- Enable two-step verification with a recovery email;
- Hide your phone number and last seen;
- Set a local passcode or biometrics;
- Review the device list regularly;
- Use secret chats for sensitive talks.
Next: efficiency
- Set a username so people can find you;
- Use folders to group chats;
- Treat Saved Messages as a drive and draft box;
- Pin important messages;
- Learn global search and hashtags.
Finally: comfort
- Configure auto-download per network;
- Set quiet hours and custom sounds;
- Switch to dark mode;
- Clear cache and set media retention;
- End web sessions after using shared computers.