hello,
right now google is considering LSI so that thing we have to take care while doing SEO for any site.can any one have ideas that which things we have to keep mind while doing SEO for LSI.

LSI a good thing for the average webmaster because if you write your pages naturally about a theme keeping the users experience in mind you will have a much greater chance of ranking higher in the search engines. LSI can really help level the playing field if you take the time to understand how to implement it.
how LSI works in simples terms.
Through word association Google is able to tell if a page with the word “Pit” on it is about a hole in the ground or a movie actor by reading the whole page referencing its database and seeing how the combination of certain words resulted in what that page was about.
If the webpage with “Pit” on it also contained words like movie, Hollywood, Brad, Angelina Jolie, Fight Club Google will know that the page deals with the actor “Pit.”
If the page with “Pit” on it contained words like Pendulum, Edgar Allan Poe, Cast, Crew, Reviews, Plot Summary, Horror Story, and Cliffnotes Google will know what to rank this page for based on the theme of the entire page not just the amount of times a particular keyword is referenced.

Thanks jayesh some of things gose bouncer here loll.i will try to search more on this topic.but one thing is sure if LSI given more weightege than keyword density of targeting keywords will not matter in SERP.what do u think?

One thing is sure. And that is that SE's want to beat the hell out of SEO's

Moreover this LSI weightage thing signals towards more relevant results rather then the results based on keyword density or other ranking factors.

but there is a possibilities to get non relavant result while searching for any kw.for exp as jayesh told when u search for "pit" there is lots of results google will give which is non relavant.they might have think on this.