How do I transfer a file from iCloud Drive directly to Google Drive?

You can easily send a file directly from your iCloud Drive to your Google Drive (or to DropBox, Amazon Drive or a number of other services) via your sharing options. Open up iCloud Drive, select a file and then tap the share button in the bottom left. Select Google Drive, then choose where you want the file to be saved by tapping on "My Drive." When you have a location set, tap "Upload." Your file will be copied to your Google Drive and you can now erase it from your iCloud Drive if you want.