Sure, next time you install get to a basic setup with updates and make an image. That won't help prevent the problems but it'll speed reinstallation. If you're reinstalling every few months there are certainly things you can do to prevent the problem. It comes down to time vs. benefit. 1) You can dig a bunch, learn a bunch, change your behavior, and still fall prey to bugs and issues that lead to a reinstall. 2) You can speed a reinstall and do it weekly. 3) Pick some combination that works for your situation.
The problem may be one or two huge effects, or the result of 1000 little cuts. The 1001st cut might have triggered one of the huge effects. The more you observe, the easier to avoid the problem next time.
Can you identify what's slow? Are any particular sequences noticably lethargic? Bootup to login, login to desktop, application launch, long or short periodic mystery pauses, continuous disk activity or every time you do something, network access. ...
Find the low hanging fruit. Big gains for minimal cost. What's your system doing? Disk access is one of the slowest common things your computer does so it's often a source of problems. You can spend a couple $thousand on a beautiful disk system and still be slow if it's being used as RAM. (I'll ignore hardware configuration errors that usually show as alerts in device manager.)
Assume a semi-stable booted system. What's the memory picture? Open task manager, performance tab. What's Commit Peak vs. Total Physical Memory? If peak has touched total physical you're low on RAM, or have too many goodies, and are swapping memory to disk. Switch to the process tab. Click the mem usage column to sort by descending. Anything up top that surprises you? Firefox extension memory leaks are a common issue. Some of the most useful extensions are the worst offenders. (i.e. adblock) Identify anything using more than 10-20MB that isn't a primary application (PShop, Office, etc). What are they and why are they huge?
Task Manager again, process tab. Click the CPU column to sort descending. Leave it open and work for a bit. Anything besides System Idle Process sticking up top for long? Why?
Look at memory and CPU again, but after the system has been used half a day. Changes? Memory usage after leaks have built up can look wildly different.
Does your unhidden taskbar look like an icon Christmas party? At some point all the goodies result in your nice new box existing to keep itself updated, scanned, protected, and displaying advertisements. Whittle things down to what's necessary. Discipline man!
If the slowdown hit all at once, can you recall anything that changed shortly before? Installs, hardware changes, etc.
Also, in the worst of cases things can live outside the "normal" world viewed by task manager and standard process watchers. That's the realm of rootkits or hardware problems & and is rare compared to the usual cruft found on boxes. Be aware those things exist but don't jump on them as the source of all ills.
Anyway, I'm rambling. Add carefully. Observe before and after so you have a chance of noticing what happened. Infinite internet monkeys have documented PC performance and fixes, so information is out there to be found.