If you use WordPress for a Blog and you think about a Theme Change for a new Look you should now some points:
Check new Themes for available Updates
Check new Theme for User Feedback
Check new Theme how often its downloaded, if often used Search Engines can handle the code
Check the new Theme some Weeks and control active the Ranking on Search Engines (like Webmaster Tools), cause bad readable Code is ranked down or broken internal links and bookmarks can forward robots into nirvana
Check the new Theme on various Browsers, Opera, Chrome, Firefox, IE, Mobile Browsers and Check Mobile Browsers on „Desktop View“
Check the Theme on various Screen width, Menu Handling, and test Browsers with disabled Java Script for barrier free handling and disabled Webfonts
Check the load Time with Browsers Analytics Tools, compress Code, Reduce Image Size
If you use Drupal or WordPress and you have a virtual Server with SSH Login you should set up a daily Backup Script to have a Snapshot of your Blogs if Hackers insert SQL Code Injections or hack PHP Sites. Cause you cant NEVER know every EXPLOIT of every used Plugin (here less plugins is more!)
Of course you can daily or hourly RESTORE AUTOMATIC by CRON your Blogs by OVERWRITE bad inserted STUFF!
Article comming soon !! .. sorry have current not enough time..
Last Time i tried to integrate a Twitter Timeline into my blog but i found out that this ranked down my blog on Google Webmaster Tools cause Twitter sub connected Servers blocking Google Webmaster Bot from reading the timeline by own robots.txt so i stopped using Twitter Integration to fix.
No Webmaster want show non indexed Informations and went back to the time of stones.. Twitter fails..