Keep your browsers and softwares up-to-date. And do not use cracks and pirated softwares!
For your browser, you need Adguard Adblocker and HTTPS Everywhere. These two extensions are essential.
You can use HitmanPro and Malwarebytes Free as a stand-alone malware scanner.
If you use USB often, maybe you should consider to use MC Shield USB Anti-Malware Tool. All these softwares are free!