If you take the correct steps when launching your new website this shouldn’t be a problem that affects you too much.You can simply add your new domain to the DNS, and people can access your site using either the old or the new URL.There’s also an option in Google Webmaster Tools where you can do this and tell Google about your changes, so they display the correct search results and direct browsers to your site via the search results.
However, some steps you can take will help you to minimize any further problems.
Setting up a 301 permanent redirect is the best and easiest step to take.Some SEO’s have suggested contacting webmasters who have links to your site on their own, but the reality is this is going to take a lot of time, plus you have no idea who is actually going to do it, the most likely scenario is that your email will receive an out loud “whatever” and placed straight in the trash.You’d need to set up the 301 redirect at server level, so that everything related to your website is redirected.You don’t want to do it one page at a time as you could end up missing out important commercial pages and lose money as a result.
You are probably looking at a 3-month timespan for all of your pages to be re-indexed by all search engines, particularly if you have a large website.That said, Google are getting better all the time at recognizing 301 redirects, while Yahoo! and Bing are also catching up in this respect.
The trick is not to panic if you see pages from both domains indexed in the immediate future, stay calm, and look at it again at the end of the 3 months.