It's a lot easier to manage browser extensions/addons if you only use one browser.
If you have to download a downloader to download a file find another source, also if a download page has multiple download links on the page and you aren't sure which one is the actual download button find another source.
Download Unchecky, it'll save you some trouble(not all) when installing programs by unchecking spamware check boxes.
Buy an external harddrive, prob just a 500gb one, and backup all important data on it every few weeks, don't leave it plugged in all the time, don't plug it into your computer when you think you've already got a virus.
Run full anti virus scans once a week with multiple anti viruses, we've mentioned a lot of good ones in this thread.
An adblocker and scriptblocker will stop a hell of a lot of things from getting onto your computer in the first place, sub to lots of ad lists and learn what scripts are usually safe to unblock.
Try to stick to reputable pron sites, there are plenty of them.
Signatures may not be bigger than 700x250, 1MB. ~Skorak