Last year I accidently found a new query in Google which seem to return URLs on a domain that Google regards as low quality, something which is very useful. I built this tool in may 2012 that returns the data. After further research it is now fairly certain what this Google query (and tool) does. It returns the supplemental index pages of a domain. So use this tool to find duplicate content issues and other indexing problems. By fixing this you maybe will rank the whole domain better.
Sorry but Google has now detected this and have disabled it ...
If high quality pages are being returned, improve your internal navigation to place more emphasis on these pages.
Remove completely pages that are not supposed to exist and/or make sure they give a 404 status header.
Put a meta noindex on pages with low quality but that you still want to keep. Remove the noindex when the quality is ok. Keep these URLs in the XML Sitemap.
301 redirect pages to similar pages with higher quality.