Q: Push Notification not working?
A: Make sure you set Whatsapp as auto start in the permission tab. (this applies to all messaging app which you want it to run on background) Still doesn't work? Pin and lock the apps on recent apps tray.

Q: How to enable developer option?
A: Tap on MIUI Version. Go to Settings > About Phones > MIUI version until it says - You're a developer!

Q: How to enable USB Debugging ?
A: Setting> Additional Settings > Developer Option > USB debugging .Slide RIGHT.

Q: Can I backup my DATA ?
A: MIUI has got its own Back up app and it's even better on MIUI 6!
Steps to be followed:
Settings >Additional Settings > Backup & Reset > Local Backups  > Backup [ Here you can select what youwant to back up ie. SYSTEM, Apps, Accounts & Contacts]