How do you verify/check if a download is safe?

Recently I have found myself wanting to download various games from the internet onto my flash drive. But since there are so many people trying to trick you into downloading viruses I was getting concerned as to the integrity of the sources and downloads, not because they looked particularly untrustworthy, but because I never used them before. I was wondering how to go about checking the downloads out before actually downloading them to prevent getting viruses. How do you do it?