1. Routine backups. All hard drives (and even SSDs) have a risk of sudden failure at any time. Age has little to do with it, though the risk does increase as time goes by. Apple provides Time Machine for free; it works well. There are other options, most of them work very well also. Pick one (or two) and use them.

2. Plenty of free space on the boot drive. By "plenty" I mean multiple gigs. I don't subscribe to the rule of "20 percent" because as drives get larger that rule gets sillier, but at least 20GB or so for light-duty users, at least double that for more serious users.

3. Run a maintenance utility regularly. We recommend the free OnyX, even though you have to work around Apple's "Gatekeeper" technology to run it. It's that good at what it does. I suggest running it roughly quarterly, perhaps a bit more often for serious power-users. AVOID MACKEEPER and similar software, they are scamware, even if you see it advertised here (Mac-Forums has *no control* over what gets advertised on the site).

Side-note: in normal use, a "defragging" of the hard drive isn't necessary, but back when major OS upgrades came out every 2-3 years I had a habit of what is called "nuke and pave," that is cloning the boot drive, erasing the boot drive, and restoring the boot drive from a cloned external. This is "poor man's defragging" and for power-users might be a good idea every year or two. There's also some programs that can handle this for you IF you have a sufficient quantity of contiguous free space (see #2 above).

4. Be aware of background programs and bad habits. More than once I've had someone complain that their Mac is terribly slow, only to discover they're running a torrenting program 24/7. Turn that off and SURPRISE, things are zippy again. A few clients who insist on keeping gigabytes of data on their desktop were astounded when I removed all that clutter and their Finder once again became fast and responsive. Know what is running in the background on your computer. Be reasonably organized with your files. Put stuff where it belongs.

5. Be aware of changing perceptions. If you originally started using your Mac five years ago to read email and surf the web, but now your shooting and editing HD wedding videos or playing high-end games, your Mac is naturally going to "feel" slower due to a combination of your changing tastes and the ever-increasing complexity of web and software technology. This is why we often say you should only expect to get about five years out of a computer investment (a bit less if we're talking about mobile devices).

Provided you have faithfully followed the steps above, your machine isn't getting slower; more likely, your needs are getting "faster." At that point its time to look at upgrades (such as more RAM and larger/faster HD or SSD storage) that will help, or perhaps its time to look at buying a new(er) machine.

PS. Memory Clean (and all programs like it) are snake oil. Either you need more real RAM for what you're doing, or the Mac will handle the memory management for you.