I have a plan to revamp one of my websites which include redesigning of the template and there might some small be changes in page names. My 40% traffic is coming from search engines esspecially . What all SEO methods I should adapt to retain by SERP's positions.
Any major redesign/restructuring of a Web site can have a negative short-term effect on the search engines. However, if the redesign has been done properly, and old links have been correctly redirected via 301 redirects to the current URLs, the impact should be minimal and temporary at best as the search engines realize that the site has been redesigned and will start ranking you properly again. Done well, you can even improve your search engine rankings. Since you're going to be dealing with redeveloping your entire Web site, now is the proper time to deal with your site's optimization for the serach engines from a development point of view (since all on-site SEO should be done before a single word of page content or line of code is written). If you don't have a lot of experience in on-site search engine optimization, information architecture and writing clean, minimal, semantic and valid markup that separates the structure (HTML), appearance (CSS) and interaction (JavaScript) into separate files while ensuring the site is accessible to people regardless of ability (or the lack thereof), you may want to hire a competent professional Web developer specializing in minimal markup, accessibility, cross-browser compatibility and usability. While I'm not available for hire at the exact moment (I'm in the process of building my own personal/portfolio site and my Web design/development resource/magazine site www.minimalmarkup.com, both of which will be launching sometime next month) I can help you weed out potential applicants who claim they know what they're doing yet don't know accessible minimal and semantic markup from a hole in the ground if you like.
Thank you for the expert advice .. What are all factors should I consider in on-site optimization in the case of revamping? Is it recommended to keep the same density of keywords and same meta tags?
Meta tags are virtually useless these days. You want to concentrate your efforts on content when rebuilding a Web site, and making sure that content (while rich in keywords) is also organic. Look in my signature for the thread "All You Need to Know About SEO" - that thread deals with on-site SEO from a developer's perspective.