Well, there's the proper way, and then there's the way most people seem to go about it, in my experience. Because I'm cynical today, I'll go with the latter:
1. Send a message to random people that just says hi. If you actually get a response, freak out and ask them what the hell they want. Ignore them if they paste your greeting back to you.
2. Spam generic "friends" group invites out all over the place. Wonder why anybody could possibly be mad at mass-invites for such a wonderful fun-loving group and tell them they're antisocial.
3. If you buy a product from someone, the merchant is your instant new best friend and doesn't mind getting roughly 40 messages a minute about whatever thought and feeling enters your head on every topic in the universe. Remember, they OWE you.
4. As a newbie, everybody in Second Life you meet is your personal tutor.
5. Send out random friend invites to every individual in your FOV big enough to hit with a right click. Make sure to get mad at anybody that declines. The person with the biggest friends list wins
SL.