Create a Twitter account.  Try to choose a short username to make "re-tweeting" easier.  Add your cell phone number under "devices" so you can send text messages to 40404 to post an update.  Be sure to setup your sleep settings so your phone won't buzz when your friends post updates at odd hours.

Get Tweetdeck.  (It will help you see what you need to see since your eyes can't be watching the Twitter stream all day long.)

Create a Facebook account. (Remember it is okay to "ignore" the invitations to add third party apps you may receive.  People won't think you are rude.)

Try Selective Twitter if you want to be able to update your Facebook status and your Twitter status all at once.  (When you post a tweet you'll add "#fb" to the tweet and it will automatically be posted as your facebook status.)

Get on LinkedIn,  if for no other reason than to reserve your name and help you dominate the first page of a Google search for your name.

I'm not sure anyone is still using MySpace except musicians and groupies.