Clean the junk
There are a multitude of utilities available for ridding a PC of junk data, applications, and malware, but there are three in particular that we find indispensable--the aforementioned PC Decrapifier, CCleaner, and Malwarebytes Anti-Malware. A fourth handy tool is Windows' own built-in Disk Cleanup utility, but it's more of a quick-and-dirty tool for wiping temporary data rather than a full-blown utility. Still, running Disk Cleanup is a good way to reclaim disk space, which can be especially helpful on low-capacity SSDs where every gigabyte is precious.
To clean up most--if not all--of the junk data from your drive, we'd recommend running Disk Cleanup first. Simply right-click on your drive in File Explorer, choose Properties from the menu, and then click the Disk Cleanup button next to the pie chart of free and used disk space. After the tool (generously) estimates the amount of space it can free up, click the Cleanup System Files button, and the window will refresh in a few moments with an additional tab labeled More Options.
Click the More Options tab, and if your system is behaving properly, click the Clean Up button in the System Restore and Shadow Copies section of the window. This will purge old restore points and shadow copies and potentially free up a ton of space. Don't clean up these items if your system is misbehaving, however, as you may need to use a previous restore point to fix things. On the Disk Cleanup tab, you'll see a window labeled 'Files to delete'. It's usually safe to check all of the options here. After selecting everything you'd like to delete, click the OK button and let Disk Cleanup do its thing.
To compliment Disk Cleanup, we also recommend running CCleaner. Whereas Disk Cleanup purges junk from Windows and associated temp folders, CCleaner purges junk from a myriad of popular apps as well. Download and install CCleaner, launch the program, and on the Cleaner tab, tick all of the Windows and application-rated temp data you'd like to remove. Then click the Run Cleaner button and CCleaner will take out the trash.
Once you've got the junk files and date cleaned from your system, it's also a good idea to run a thorough malware scan to purge any tracking cookies and potentially malicious malware. Download and install Malwarebytes Anti-Malware--the free edition will do just fine--and run a Full system scan. The first time you launch the program, you'll be asked to update its definitions. Perform the update and then follow the on-screen prompts to complete a Full system scan. Even on a well-maintained system that's behaving normally, you may be surprised by how much crud Malwarebytes Anti-Malware can find on a system.
Disable unnecessary startup items
CCleaner is also a handy tool for disabling programs from starting with Windows and plug-ins from launching with your browsers. Microsoft has built-in tools to do the same things, namely MSCONFIG and the Startup tab in the Windows 8 Task Manager, but CCleaner makes the process much easier in our opinion.
Disabling unnecessary startup items is one of the quickest and easiest ways to improve the overall the performance of a system, especially an older or underpowered system. As we've already mentioned, any application or add-on that launches automatically consumes memory and potentially CPU time. Killing those apps and add-ons frees up those resources to do the things you actually want to do with your PC.