Quick Tips:

How to Get Rid of Android Ransomware?

Boot your device into "Safe Mode," as it boots your device with default settings without running any third-party applications and allowing users to delete malicious software.
To uninstall the ransomware from your device, you need to first remove administrator privilege by going to Settings –> Security –> Device Administrator and then select ransomware app and deactivate it.
Once this is done, you can again go to Settings –> Apps –> Uninstall ransomware app.
(optional) If above steps not working, you can try to use an Ransomware Decryption and Malware Removal ToolKit from Google Play or search on the www how to get rid of it.

General words aboout it and already can lower the attacks:

Don't install apps from outside of the Google Play Store or F-Droid (no, also not from Aptoide!)
Don't grant administrator privileges to apps unless you truly trust them!

Broken screen? How to backup your data from a broken Android (hostilejourney.com)

Never ever open attachments from unknown sources.
Never click on links in SMS or MMS messages sent to your phone.
Even if the email looks legit, go directly to the source website and verify any possible updates.
Go to Settings - Security - Turn OFF "Allow installation of apps from sources other than the Play Store" option.
Always keep an up-to-date Anti-virus app on your Android devices.
Avoid unknown and unsecured Wi-Fi hotspots and Keep your Wi-Fi turned OFF when not in use.