I have noticed that although most of the pages on my site are indexed, most do not rank very highly or come up anywhere near the top of Google when searching. However I have also noticed that new pages I add to the site (the latest 20 of which are linked to from the home-page), are indexed straight away and fly to the top of Google. After some time (usually a few weeks, sometimes as quickly as a few days) it seems they drop from the top.
Therefore to make sure that some pages are always indexed highly I could in theory simply keep changing their URLs and include a link to them on the homepage. In tests this seems to work very well and the pages are again at the top of Google search results. Can anyone tell me why this happens, why new pages (or pages with new URLs that appear to Google to be new pages) immediately top the search results? Also is there any reason why changing the URLs on a regular basis to keep these pages at the top is a bad idea (apart from the obvious broken links, although I could create 301 redirects)?