1. Don't do anything permanant without asking someone who knows A LOT about Bitcoin. Search the Bitcoin forum at http://now.cur.lv/bitcointalk and, if you can't find an answer, ask in the newbie or technical section. Remember to search the stickies before asking anything, since it may have been answered.
2. NEVER delete your wallet.dat file unless you have moved all bitcoins out of it, or they are definitely gone (unless by some astronomical coincidence someone else gets the same key)
3. Make copies of your wallet.dat to store offline. It contains all of your keys, so while you only need one, you are sunk if all are lost.
4. Backup your wallet.dat file before you try anything that involves any tweaking. This includes encrypting it. There is no way to get the password if you lose it.
5. Never assume anything while asking questions in the forum. While there could very well be people tricking you, they probably won't. There's nothing to gain from looting a new person's probably-empty wallet.
6. If you don't trust the computer, keep paper wallets and treat them like disposable currency. Set certain denominations and manage them. Keep copies anyway, but remember that all identical ones have the same coins. When you need to spend a bill, give the key to that bill instead.
7. Remember that you cannot have your coins stolen just because someone knows an address. In fact they need it to send them to you.
8. If you know how to get HTML source code (use ctrl + u) then get the one from http://now.cur.lv/bitaddress to make paper wallets. Save it and run it while not connected to the Internet. Looks like a website, but it is actually an offline page. Still, it does what you need it to do.
9. Never use or accept Paypal for Bitcoin trades.
10. NEVER USE OR ACCEPT PAYPAL FOR BITCOIN TRADES!
