There are two ways to do this. You can link Twitter to Facebook, or Facebook to twitter. The choice will usually depend on which service you use the most.
If you use Facebook more, link to your Twitter account from Facebook. This is how you do it.
If you’d like to link a facebook page you’ve created, go to the following link and follow the instructions:
If you’d like your regular facebook profile status to post automatically to your twitter account, it’s a bit trickier. You will need the help of a third party app. Instructions can be found at the following website:
Or, you can manually tweet from facebook by using the twitter app on facebook which can be found here (hint: click on “Go to Application”):
If you use Twitter more, link to your Facebook account from Twitter. This is how you do it.
Go to the link posted before:
Once you are signed in, click on the button in the top right that says “+Allow Twitted to update your facebook status”.
A word of caution. Try to have the communication go one way only. You don’t want to get into a situation where you are doubling your postings or creating weird loops. If you’d like the versatility of using both, use the Twitter app only and post from one or the other.