These days, we try different ways to boost up our smartphones performance and thus, it is important to trace down what you might be doing wrong with your devices while making such attempts.
Killing apps manually: In years, Android has evolved a lot and it's now much efficient in handling tasks running in background. Note that RAM sitting idle is just wasting your resources. Thus, Android now automatically feeds RAM by killing less priority background apps, when required, without using any third-part task manager apps.
Side-loading apps from unknown or untrustworthy sources: Yes, you don't need an antivirus app unless you don't side-load apps. However, Android has APK Files can be easily tampered to inject malicious codes, which in turn can invade your privacy. So, make sure you install apps only from trusted sources like Play Store.
Installing More Than One Security (Antivirus App): These apps do no any better than draining your device battery. And it is unnecessary for Android users to download such apps, as Google has covered it for you. Installing apps from Google Play Store doesn't side-load any third party app that would inject a virus in your device.
Not Reboooting Your Phone: A smartphone should be rebooted once in a week or at least in a fortnight. This will clear up unnecessary things holding on to your memory and give the device a fresh start.
Using app cleaner to clear cache: Remember, the cache data is important for an app to function. Apps use this cache data for quick performance. For instance, WhatsApp caches data is profile pictures of the contacts and media shared, as a result you don't have to reload them every time when you open it. Also, even if you clear the caches data, just to free up a few extra MBs, they will start rebuilding after you delete it.
You don't need an antivirus app unless you don't side-load apps