For a major update, resubmit your sitemap.xml via GWT. For day to day updates, just revise and upload sitemap.xml to your site root. Don't resubmit. Google will retrieve the file regularly, if it exists (has been submitted at least once) and it is valid.

Check your status regularly for errors or issues and fix them. Google will discover the repairs on their own.

Be sure to revise PRIORITY to match 'time erosion'; that is, lower the priority as items age, and give higher priority to new, recent, and still current (or relevant) items. This way, your important pages will find their way to the top of the heap.