If you haven't started dedicating the second Tuesday of each month to security updates, it might be time to start. Today is Patch day, and it's a busy one for Microsoft with 11 security bulletins (and three new security advisories).
According to the summary post, today's 11 bulletins fix 24 vulnerabilities in a wide range of Microsoft software, including Internet Explorer (IE), Windows, Office, Exchange, Lync, Sharepoint Server, and more. Microsoft rates five of the bulletins as Critical, and the remaining six as Important.
While it's hard to give priority to updates when there are so many critical ones, Here're my recommendations. I'd apply the GDI+ update (MS13-096) first, since it fixes an zero day flaw that has been exploited in the wild; install the Exchange server update (MS13-105) next, since attackers can exploit its flaws just by sending you an email; and run the IE update (MS13-097) third, as it fixes vulnerabilities that bad guys can leverage in drive-by download attacks. You can apply the remainingCritical ones in any order you like, and finish off with all the Important ones. Whatever order you pick, I recommend downloading, testing, and installing these updates as quickly as you can.
As far as testing goes, I really recommend you test updates first, especially server updates like the Exchange one. You don't want a bad patch causing downtime for your production environment. Creating virtual copies of your production servers provides an easy way to test patches in a virtual environment.
As an aside, today is also Adobe patch day, and Mozilla released Firefox 26 to fix security issues as well. You can learn more about those updates now using the provided links, but I'll post more details about the Adobe one later.