Stop Running So Many Apps at Once
Take a look at your system tray (or menu bar). If you have more than a few icons there, you have too many. If something is running that you didn’t start, take it out of your startup queue. If you don’t know what something is, find out if it’s something you really need. If it’s something you know you don’t want, then uninstall it completely.
Stop Installing Crappy Programs
Sometimes, a single app can bring your entire computer to a screeching halt. This includes programs that run unnecessary services in the background, hook themselves into the Windows Shell (like Windows Explorer plugins), or are just plain slow.
If you’re skeptical about an app, ask yourself: Does your computer run faster when you close that program? If so, then surprise: you should probably ditch it. “Crappy” doesn’t always mean “sketchy,” either. After all, we’d consider iTunes a pretty crappy app since it injects itself into every corner of your computer and slows it down a ton when you run it. If you can’t live without it, at least use a different player for listening and only open iTunes when you have to sync.
Stop Bloating Up the Programs You Have
The more work you heap onto an app, the slower it’s going to run. Your music player will be slower if you have a huge library, so clean out that music you don’t need. Your browser will struggle the more add-ons and plugins you install, so clean it out to speed it up. The less work you make your apps do, the faster they’ll run.
Perform Regular Maintenance
While there are a lot of maintenance myths out there, you do need to perform a little regular maintenance once in awhile. Most of it involves keeping your software updated, your programs list trim, and your temporary files emptied. Check out these guides to Windows and Mac maintenance for more info.
Of course, this all assumes you have a relatively new computer that can handle the work you need to do. If you’re trying to run the newest version of Photoshop on a 10 year old machine, no amount of responsibility will make it run fast—you’ll need a new computer (and you can repurpose that old one). But, barring really old hardware or other special circumstances, you should be able to take any computer and get it running fast again with a bit of care and common sense.