My site had been on Page 1 (position 3-5) for several years, but recently has backslid all the way to page 3. There were no major updates or site changes during the periods the position dropped. I would like to analyze my site and figure out what's wrong... but don't know where to begin. Are there any reputable tools (or decently-priced LEGITIMATE SEO companies) that can perform an analysis and give me a list of things to improve? I have the basics covered - W3C error checking, site speed, caching images, etc. What would you personally use, if you didn't have the skills/time to manually analyze a site? Any suggestions would be much appreciated!
There has been a recent Google Panda update focusing on thin content/low quality pages. If you have any remove them or fix them. Check the bounce and exit rate of your pages with Google Analytics. There has also been a recent Google update to kill backlink from private blog networks. If you benefit from any, shake them (i.e., disavow them). I would start with that.
I agree with Poupoupidou. Also if you need to make some analysis there are free checkers online. But you have to make sure your site is inline with the Panda update because even your site ranked number 1 for many years, a specific Google update can cause it to go as far as page 5.
More often than not these days it has more to do with links than anything else. Yes, Panda is a problem for some but if you have a somewhat decent site this should not be a problem at all. Backlinks on the other hand are a problem, I suggest using http://linkdelete.com tool on their homepage which looks at your links and tell you how many bad links you have and your overall risk factor score. A helpful tool I use when looking at new clients and determining how much link cleanup will need to be done. Another good tool is the Panguin tool found here: http://www.barracuda-digital.co.uk/panguin-tool/ This tool can tell you what penalties you were hit by based on your analytics data, very helpful for identifying algorithm issues. Finally I suggest looking at Webmaster tools to confirm you don't have a manual penalty, sometimes people over look this factor which is critically important.