SERP = Search Engine Rank / Position. This is where you actually show up in the search results for various words or terms used to search for and find your site. This is something no one has real control over as each SE has its own way of ranking sites when someone searchs. Search Results are also very fluid. You can be top position one second and the next be #10 as the fluidity of the net alters your search results.
Sometimes your SERP is due to an error in your site or a change in that of your competitor. SERP errors can be discovered and fixed if they are within your own site. If they happen to be because of significant changes in the other sites all competing for the same search there is not much you can do other than make significant changes or additions to your site.
SERP can be affected by all kinds of things. The first and foremost is the code used to make your site. If your W3C complaint in the code of your site then your good to go there. You can look at how the SE’s see your site. There are a number of ways to do this. One of the simpelest is to click within your page and do a select all and copy. Then past that text into a NOTEPAD document and it will show you how the SE’s see your site. The text and content is read just like what you see there. If it makes sense to you then it makes sense to the SE’s. If you site is coded so that your content shows at the top part of the page and reads properly then its time to look at the content and how often it changes. The SE’s notice how often your site changes. Everytime something changes, the SE’s take notice. The addition of materials to your site on a regular basis shows the SE’s that your site is growing and thus becoming more important as a search result which increases your SERP.
Sparky