In the world of SEO, changing a domain name maybe like a sin. You can loss visitors, page rank, mutual incoming links and Alexa traffic rank. You should not do this unless your domain is have a pattern like this “10 worst domain names” or because of branding issue.
SEO FAQ by Jill Whalen says there is a way to minimize traffic lost caused by domain name change. Instantly you just need a 301 permanent redirect to tell search engine that the old URL is no longer to be used, so they can update their index. It can be easily done by putting it in a .htaccess file, but it is not always the best choice.
Using 302 “temporarily moved” is the best choice instead of 301. The old URL will remain on Google’s index and search rankings and Visitors will go to your new URL after clicking your link. After your new URL starts showing up in the search result, you can change to 301 permanent redirect for your old domain.
More detail can be read here.