...on Omegle? xD
Its not as easy as it sounds. Obviously a stranger you are talking to doesn't know anything about you. But try to have a serious conversation with someone (takes about 10 goes at starting a chat to find someone decent willing to have a proper conversation) and make them believe you are this person you are actually not. For example I will try to be a 19 year old girl from New-York City. When IRL Im first of all a male, in a different age group, and I live on the other side of the Atlantic =)
The first trap I fell into was when a person asked me for a picture of "myself". It took me around 5 minutes to find a nice picture on a social website (Facebook/MySpace/Bebo etc.) .
Here are the photos I used then and all the other times I pretended to be this person:

(damn she doesn't look like 19 at all here)

The second test came when another person asked me the time in NYC. This took me 30 seconds to find out. I went to Google and searched for "ny webcam". The very first site featured a webcam and luckily it had local time underneath :)
Some other things I've been asked that I didnt't know:
-What is the ball called in American Football
-Exact place in NYC I live in. I gave a name of a district but it didn't suit the person. (o_O)
-What I study. Be careful what you say here as the person might ask you extra things about the subject that you mightn't have a clue about. So don't say you want to be a brain surgeon =)
-My MSN :) . If you really want to take this far, set up a fake MSN, because lots of people want to talk there. I couldn't be bothered myself though.
-My boob size. xD Really random.
I always start a conversation with a/s/l and expect others to do the same, which most do. It gives a basic idea to whom you are talking to and how to behave. To most people its obvious what a/s/l is, but since I love n00bz so much Im going to elaborate:
a - is your age.
s - is your gender
l - is where you are from
An example of an a/s/l in my case is 19/f/ny. Pretty easy huh?
After some time and some epic fails you will eventually live in to the role of this made-up person. Its really fun if you do it right and trains your lying skills :D
Thanks to:
Omegle, a random girl whose photo I used, all those I talked to.
Sub-Zero