Use your brain, common sense and trust your gut feelings. If you wouldn't share info with someone you met in real life, don't do it on the net.
If it sounds too good to be true, it usually is false-like downloading all the free music or videos you want without taking a chance on getting caught in some way. There are some places to get an occasional song from a popular artist, or possibly an album from an indie group.
I recently just started playing Scrabble via Facebook. But, I heard about it a while ago, before privacy and security was improved. Someone I knew well and trusted invited me, so I went for it.
Keep in mind very few things in life and yes, even on the internet are free. Most sites are free because businesses are paying for ads and information about you, generally without your name or personally identifiable information like your social security or phone number. But if the terms of service on a reputable site say otherwise, your privacy may be at risk. If an illegal site run by criminals, say, "Unlimited Black Ops, latest version", exactly like the one sold in stores was offered free, why would that make sense?
Be Safe so you can keep having fun, online and in real time. Oh, and the best of life is in real time, so get offline and face to face as much as possible.
A lifetime of experience and people I care about.