Hello and welcome to my User Tip
Although you might have heard that "Mac's don't need maintenance" they actually do in sense to keep things more or less in line or the machine can become a mess through a users inaction to keep things tidy and updated.
So I'm going to share what you can do to keep your Mac running fine.
1: Apple Menu > Software Update (repeat until clear) - fixes issues and security problems in Apple provided software.
2: Third Party Software
Open each and search for a update button or visit the developers website and verify the version or uninstall if issues develop according to the developers directions (do no use AppDelete type programs).
A warning flag should go off if your auto-updating program (like Chrome or Firefox) is not the current compatible OS X version. You have a further issue to fix. ..Step by Step to fix your Mac
Check for browser add-ons that if there are any updates for those.
Anti-malware software, update the definitions to make sure it's current.
Note: AppStore software is usually behind about 4-8 weeks. Some developers are not carrying on AppStore anymore so their software might not be current there. Install software directly from the developers website if it's there instead, it will have it's own updater and be faster that way, especially for any software that contacts the Internet routinely, like Opera or other browsers or mail programs.
3: Third Party System Preferences files and Finder menu items - don't forget updating those.
4: Third Party Web Browser Plug-ins - This checker can assist enormously: https://www.mozilla.org/en-US/plugincheck/
5: Reset Safari and all web browsers caches files located in each browser's preferences.
6: Reset Flash and other web browser plugin caches find out where they are located per browser plugin
7: For Privacy. Run the free CCleaner for the Mac: https://www.piriform.com/mac/ccleaner
8: If running another operating system in BootCamp or virtual machine software, revert to a earlier secure snapshot and do all the updates and cleaning.
9: Update your more immediate backup system, either TimeMachine and/or bootable clones if they are disconnected.
10: Do not update your longer term-
-disconnected bootable clone backup until another few weeks have passed to make sure all your software is working as intended, you might have to revert to this earlier machine state to bypass new issues. Most commonly used backup methods
11: Optional scrubbing:
If you have a boot hard drive you can opt to scrub the deleted files off the drive and cure future bad sector issues at the same time by using Disk Utilities > Erase Free Space > Zero option on the Macintosh HD. It will take some time to complete and isnt' necessary, but can assist reduce the possibility of future problems.
Never move a computer or a hard drive while it's running. It's a big cause of many issues on these forums.
SSD's can't be securely erased or scrubbed. How do I securely delete data from the machine?
12: Check for recent security issues: Security Issues Warning List
If your running OS X 10.8 Mountain Lion,
Right click or control click on software that won't run or install that you trust the source of, this will bypass Apple's Gatekeeper and shouldn't be required to do so ever again.
1: Run the #12/#13 OnyX cache cleaning /repair routine (do not clean the log files, you may need those) and reboot. ..Step by Step to fix your Mac
2: Check your router makers site for firmware updates for your router and apply, they fix security issues. WiFi security issues, at home and WiFi hotspots
3: Update your long term backup/bootable clone if there wasn't a OS X or third party update in the last week or so to make sure it's running as expected.
Do all the time:
1: Don't let your boot hard drive get more than 50% (best performance) or more than 80% filled. Do not ignore the warnings your boot drive is getting filled
2: Don't let your boot Solid State Disk or Flash drive get more than 80% filled. Look in Utilities > Activity Monitor
3: Do not install software or browser plugins from unverifiable sources. Especially if there is no means to get into physical contact with the developer. Security Steps and Behavior
4: Do not visit risky web sites or ignore "Safe Warnings" as Mac's can also be attacked at malicious web sites. Ideally, use a virtual machine operating system you can purge in a few seconds by reverting to a earlier snapshot. (Linux also can be used and it's free)
5: Do not install software promising to "speed up your Mac" Learn how your machine works here: Why is my computer slow?
6: Keep a clone backup of each Mac on a powered external drive kept offsite to prevent against fire, theft and acts of man. Most commonly used backup methods
What you don't need to do:
1: Regular Defragmentation -
Needed only for hard drives (not SSDs) and OS X does it's own so you don't have to unless it's been upgraded or in a very rare long time, then if it's required there is a very safe and long lasting method to go about it here: How to safely defrag a Mac's hard drive
2: Run restrictive or always on anti-virus.
Apple has their own installed and the free ClamXav is good enough for the Windows malware that comes on files in OS X. (but don't affect OS X)
Uninstall the always on anti-virus using the developers uninstall method as it likely installed files into OS X itself, thus needs special uninstaller to remove it.
3: Don't use MacKeeper, it's a burn.
What you should consider having done:
1: Cleaning inside of the machine of dust
One can greatly extend the usable life of their computer if the dust is routinely cleaned out of the machine, especially the cooling fins where it gets clogged at.
Inquire with Apple or Apple Authorized Repair about having the dust cleaned out of the machine at least once a year and determining from that how often to have it done.
Do not open the machine unless it's one of those machines that are user service allowed or you will void your AppleCare/warranty.
Enjoy your Mac.