I'm working on a very competitive keyword and trying to rank my page well for almost 9 months now. At the beginning the page was nowhere to be found and it first appeared on results on page 40+ (400th place). Since then lots of work has taken place: on site (titles, tags, etc), we created a blog and kept on adding unique quality content, and also we started a link campaign to gain links from relevant sites.
For the last 4-5 months the site's position on Google is following a strange pattern i have never encountered before.
1. The site stays at the same position for about 3-4 weeks.
2. The site loses about 10 positions for 3-7 days.
3. After that it gains about 30-40 places.
For example, since mid November my site was on page 7. Last week it moved down to page 8, and today I'm seeing it on page 4.
Not sure if this pattern is of any importance or meaning, i just thought it would be useful to share it.