This is probably my first constructive and hopefully useful post, but I'm reading this forum from the beginnings, so hello everyone .
Anyway, first tip is for webmasters that don't live in US. I'm from Europe, Balkans, and when I go to google.com, I'm redirected to google in my language in my case thats .si, google.si. So why is that bad? Well, when you do searches in .si google, you don't get same SERPs displayed like some surfer in US would see. So that can be a problem if you want to rank good for some keyword and you don't really know if you see right SERPs.
What I usually do is I visit google .co.uk version, thats UK version of google site and it has similar SERPs as US visitors would see. So if you are not from US or UK try google.co.uk for more accurate SERPS.
Second tip is about backlinks, I'm really obsessed with backlinkwatch site and I spend quite a lot of time on that site exploring or should I say investigating my competitors backlinks. If you use backlinkwatch, pay attention to this kind of links ( http:// www . bla bla.com/2006/11/28/some-post-title/) that are blog links and probably comment links so if you see this kind of links when you investigate your competitor, that probably means he found a blog to post his link in comments, whats also important is /2006/11/28 you see the year .. 2006 that means that post is 3 years old, so it probably has some PR and thats always helpful.
Hope you get some ideas