It probably seems logical that you should avoid moving servers if you can. Unfortunately, sometimes you just can't avoid it. In that case, or in the case that you are setting up your server for the first time, there are some things you can do to make your experience more trouble-free.

Action	Status
Email Accounts setup (individual accts, catch all, bounce, postmaster)
Customized 404 page(s)
php.ini file modifications if necessary (timeout, default index, magic_quotes, etc.); if moving servers, download copy of old server php.ini file as reference
Web analytics setup (may need to move log files from old server if moving servers)
FTP / Secure Shell accounts
Password protect relevant directories
Apache settings (no viewing directories, etc.); if moving servers, download copy of old server http.conf file as reference
Test code for CSS, HTML integrity via W3C
cron jobs
Verify IP address not blacklisted; attempt to whitelist if appropriate (http://www.mxtoolbox.com/blacklists.aspx)
SSL certificate
Database(s) setup, including maintaining same username/passwords or changing any scripts that access DBs if username/password changes
Relevant 3rd party scripts installed (e.g. phpMyAdmin, openads, AWStats)
Run a complete DNS report (http://intodns.com/, http://www.iptools.com/, http://www.pweb.cz/en/dns-test/ http://www.checkdns.net/quickcheckdomainf.aspx) and a reverse DNS check (http://postmaster-us.aol.com/tools/rdns.html)
Run SPF / SenderID test (http://www.openspf.org/Tools, http://www.vamsoft.com/spfcheck.asp, http://senderid.returnpath.net/how.php; or simply send an email from the domain with SPF to test to check-auth@verifier.port25.com. An Authentication Report will be sent back to the email account inbox after a few minutes with complete details and results of summary, SPF check, DomainKeys check, DKIM check, and Sender-ID check.