How to get the file ID so I can perform a download of a file from Google Drive API on Android?

In my opinion the easiest and fastest way to get a Google Drive file ID is from Google Drive on the web. Right-click the file name and select Get shareable link. The last part of the link is the file ID. Then you can cancel the sharing.

This script logs all the file names and ids in the drive:

// Log the name and id of every file in the user's Drive
function listFiles() {
  var files = DriveApp.getFiles();
  while ( files.hasNext() ) {
    var file = files.next();
    Logger.log( file.getName() + ' ' + file.getId() );
  }
}  

Also, the "Files: list" page has a form at the end that lists the metadata of all the files in the drive, that can be used in case you need but a few ids.

Well the first option I could think of is that you could send a list request with search parameters for your file, like title="File_1.xml" and fileExtension="xml". It will either return an empty list of files (there isn't one matching the serach criteria), or return a list with at least one file. If it's only one - it's easy. But if there are more - you'll have to select one of them based on some other fields. Remember that in gdrive you could have more than 1 file with the same name. So the more search parameters you provide, the better.