Until the end of this month you can pick up a 3 month xbox live subscription for just $9.99 which is half of the regular price. The special price is only for people who do not already have xbox live gold. However if your renewal date is before the 30th you can cancel and pick up the cheap price before it is gone.

If you only have a silver subscription all you have to do is log into your xbox live dashboard or the xbox live site and subscribe.