I have many keywords used to be the first, buy I found yesterday that the all dropped to the second or third positons. I did not update my webiste or find backlinks in the past two months Then I loged in to GWT, and found that backlinks to my pages all decreased many. Could the ranking dropping be caused by this? Now I wanna add more backlinks, not sure if can get to the first again.
Take a look: http://siteanalytics.compete.com/sparepartswarehouse.com+babatek.com/ You are competing with a website many times your current level. Google favors large websites such as this over smaller ones, so it's likely a Google algorithm change was introduced. Also, a big company such as your competitor is likely able to devote a large portion of their budget to SEO/SEM, so you are in for an interesting ride if they deem your keywords worthy enough of their time.
I recently noticed drops on two of our main keywords from top 5 positions down to 11 and the other keyword nowhere to be found. We are a fairly new site and this seems to be a normal occurrence but was disappointed to see progress to #1 then back down. Any idea of why the Google webmaster tool's would show such constant movement?
There is almost always going to be some change and movement both up and down as time goes on. I would pay more attention to overall site traffic then any specific keyword ranking, unless you want to concentrate your efforts competing with others for the same thing.
I think that it could be loss of back links of your website. Do off page, i mean to stay do link building for some back links, you are again on top.