Though this is very rare that we move our established website to a new domain, but those who initially start their site with Blogspot or Wordpress platform have to face this problem when they move it to new domain. No matter what the reason is, with a new name you have to establish everything for you again. If not correctly done, this will cock up all web reputation that you have made in years. Here is a list of few must-to-do things to retain all the ranking and reputation of your old site.
1/4. Don't Dissolve Your Old Site
Since it will take some adequate time to get established your new domain, till then hold down the old one for at leas 6 months. It can be used to redirect all traffic coming to the old site to the new. People who come to your website through any externally linked contents or through search engines can be automatically redirected to the respective new URLs without breaking their interest. Preventing a 404 (Page Not Found) error is our main motive.
2/4. Complete New Website and Change Internal Links
Fully complete your new website and check that there are not any broken links. You can take help of Xenu, a popular link checker program. All internal links should be very carefully transformed to point URLs according to new site structure. If you have totally moved all older articles also, then again verify that no content should link to articles of old website. But if you are continuing from last post of the previous website, then it is fine to link your older contents. All this should have been completed before submitting the site to search engines.
3/4. Submit to Search Engines
As you had done with your old site, now it time to do again with the new one. Submit your sitemap to various search engines so that they start crawling your new contents without any delay. Register with them if they offer some webmaster programs like Bing, Google etc. A Webmaster tool offers you the best way to monitor your site progress in search engines. They are helpful in detecting any health issue with your website, and also in analyzing search queries for which your site appears in SRP.
4/4. Redirect Search Engines to New Pages
[MOST IMPORTANT]
Use a 301 Redirect to permanently redirect all pages on your old site to the respective page on new site. While real visitors get redirected silently, this has specific meaning to crawlers. When search engines encounter a 301 redirect, they understand that the page has been moved permanently and they index the target URL by omitting the old address. So, don't be lazy and never redirect all pages to the new home page. This will be very bad for your visitors as well as search engines. Always do page-to-page redirect (where each old page gets redirected to the corresponding new page). Definitely you have to do more work, but it gives your users a consistent and transparent experience.
I hope if would correctly do these for things, your web reputation will not fall neither your traffic will be hampered.