Section 1: General Security Practices
It's a tricky world we live in with our lives becoming more and more entangled in computers. No matter how security conscious you are, you can't deny the most prevalent crime you face by simply using the Internet:
Identity Theft. All of the sections of this guide play some role in reducing the chance you have of going into a job interview, trying to get a loan, etc. and are denied because they did a background check on you and you suddenly become aware of having a warrant for your arrest in a state or country you have never been too.

That has happened more often than you think.
Be cautious of the information you give out:
There are many different types of people who use the Internet: using the sites for their intended purpose, using sites to market for their business, using sites to make a quick buck, and using sites to steal information. The first example is the majority of the population, and the last three all have severe consequences for people who aren't aware of this.
When you use the Internet, look at every website as a test of trust between you and a real person. There are plenty of websites out there which put on the appearance of a legit business to store your personal information for their own marketing plans (like using your name and E-mail to spam you with their 100's of their Viagra or weight loss offers), or simply sell off their lists for a quick buck to other companies who will spam your E-mail with those offers.
Even on reputable websites like Runescape, there are people who will see things you say in the game or on the forum and remember it for later to use
social engineering to gain access to your account or find you on other websites for more malicious uses.
Don't click on suspicious advertisements:
If you are viewing a website and see an advertisement that makes you think something like, "Are you serious?" or "No way!" then don't click it or even move your mouse cursor anywhere near it.
There are many advertisements which use flash or JavaScript to operate. If you get your mouse cursor near it, they will make themselves larger, start a movie playing on the screen, or open up other websites. Besides being annoying, they often will be from malicious advertisers that will redirect you to sites which may compromise your computer in one way or another.
In some instances, I have had advertisements open up another window (by just loading on the web page and no interaction from me started it) and that window "looked" exactly like a traditional Windows XP file window that you would use to access folders on your computer. That then "attempted" to install a Trojan on my computer while also changing it's image to show an alert saying that my computer has been compromised and I need to update my virus protection. Needless to say, I use Kaspersky Internet Security 2010 and it blocked the Trojan and removed it. I then closed the entire browser because I didn't care to risk it anymore. Oh, and that advertisement happened to load from Facebook and again on a couple other Web 2.0 websites that used DoubleClick and AdWords to manage their advertisements (both trusted companies ran by Google).
Have secure passwords:
Did you know that the most common password is 123456? I kid you not, a good percentage of people use it. Take a moment and think about how common your password is. Do you use words from the dictionary, repetitive number sequences, your pets, your loved-ones birthdays?
A good password is one that is around 10-14 characters in length, has at least 2 special characters ($, ^, &, @), 3 numbers, and upper and lower case letters. Now, not all websites will allow all of these, but get as close as you can.
Don't leave your passwords written down, under your keyboard, on sticky notes, in your E-mail, saved in your browser's "remember your password" option, within identity management services, etc. The most secure place to leave your passwords is in your head. If you absolutely "must" have them stored somewhere then open up an image creation program like MS Paint or Photoshop and write them there and save the image as a PNG file and then zip that image into a ZIP file with password protection to open. The file names here should not be obvious like "passwords". A second option would be to print out all your passwords and keep them locked up in a safe somewhere.
A good way I like to create passwords is take a noun, verb, 2-4 numbers, and 2-4 special characters and create an acronym out of them.
Example:
Noun: Zebra
Verb: Fall
4 Numbers: 2, 9, 4, 5
2 Special Characters: @, &
Take each letter, number, and special character and jumble them up into an acronym that makes sense if you read it in LEET.
Result: Z&4l2F;@be9rala5
English translation: Zandal to fat benign ralas
It doesn't exactly make sense, but any program that needs to crack passwords will either run out of successful attempts and be caught by the server, or spend days in the process as there are just too many possibilities for a password of that strength.