The following instructions were written for the Resource perspective, but they will also work in many other perspectives.
To create a new, empty XML file, follow these instructions:
The XML file appears in the Navigator view and, by default, automatically opens in the XML source page editor. The XML source page editor offers limited functionality compared to the XML editor, so before editing the file, you should close it, then right-click the file in the Navigator view and click Open With > XML Editor to open the file in the XML editor.
To make the XML editor the default editor for XML files, select Window > Preferences > Workbench > File Associations, then select *.xml and XML Editor from the Associated Editors list. Click Default, then click OK.