Another helpful thing to do is this: After you establish an account with the new hosting provider and after you upload all of your files/dbs there, but *before* you switch the name server records with your domain registrar, it's best to make sure the site is operational on the new server. The simplest way to do that is to temporarily edit your hosts file and aim your domain name at the new server's IP address.
This will allow you, and only you, to browse to www . yourdomainname . com to see how the site is behaving on the new server. This gives you the opportunity to work out any bugs before switching name servers and exposing the world to your untested site that now lives on the new server.