When a user clicks on Add Document, a File upload dialogue is displayed and the user browses for a file. Even though he clicks cancel button after file upload, workflow is triggering. How to avoid this behavior when user clicks on cancel button.
You need to trigger the workflow on file modified, not file created.
Essentially, the process is: SharePoint uploads the file, then checks it out to the user who uploaded it until the required file metadata has been filled out, then update the file with the metadata.