Website Migration or Redesign SEO Guide

Will changing our web site affect our search engine rankings?

As with many SEO related questions, the short answer is, "It depends". 
The first thing to clarify is what "changing" means.
Outside of changes to content, keyword usage and incoming links, common changes to a web site that affect search engine visibility include: Changing domain names, content management systems, design or web hosts

Here are five rules to keep in mind when migrating content to a new CMS.

Migration steps to insure ranking change has minimal impact

1. Implement a 301 Redirect
   Use: If you have permanently changed the URL structure on your site (via either optimization change or CMS migration), you will want to implement 301 redirects from the old URL to the new URL.
   • PHP: Redirecting with htaccess
     The syntax for a basic 301 redirect is in htaccess:
     Redirect 301 relative/path/to/oldurl/ http://www.domain.com/newurl/
   •  ASP.NET: Redirecting with ASP.NET and IIS
     you can implement 301 redirects using ISAPI Rewriting modules, products like UrlRewriter.NET which is discussed in Chapter 3, "Provocative SE-Friendly URLs," of the book, Professional Search Engine Optimization with ASP.NET: A Developer's Guide to SEO, or from within your ASP.NET code by setting the appropriate header data.  When using ISAPI_Rewrite, redirecting is implemented similarly to URL rewriting, except that you specify a redirection status code as a parameter. The following rule does a 301 redirect to Catalog.aspx when the initial request is for Catalog.html: # 301 Redirect Catalog.html to Catalog.aspx
     RewriteRule ^/Catalog.html$ http://seoasp/Catalog.aspx [RP]

     If you want to implement the redirect yourself, you need to manipulate the response headers using the Response object provided by your current HttpContext object. Here's how to 301 redirect Catalog.html to Catalog.aspx yourself:
     if (context.Request.Path == "/Catalog.html")
     {
     context.Response.Status = "301 Moved Permanently";
     context.Response.AddHeader("Location", "http://www.example.com/Catalog.aspx");
     }
     Explanation: The first URL should be a relative path to the old URL and the second one should be an absolute path to the new URL.

2. Set Custom 404 Page
   404 page should  include  links to popular sections & archives, a link to their own search engine, site map links and of course, a link to homepage. Example: http://searchenginewatch.com/1
3. Look for broken links that may have come up as the site architecture changes a bit.
4. Create a site map for your visitors so if they feel lost, they have a listing of all the pages on the site.
5. Keep the title tags the same as much as possible to keep any rankings.
6. Consult with your SEO
   Before you make the new site live so he can help prevent any issues.

Aditional info can be found at:

• http://googlewebmastercentral.blogspot.com/2008/04/best-practices-when-moving-your-site.html
• http://www.youtube.com/watch?v=OoJAcUEasBU&feature=player_embedded