My xbox live ran out and so I went onto the website to have a look around and to my delight found that they were offering a free month trial.
1.) Visit the xbox website and sign into your account.
2.) Click My account in the top right
3.) Go into the subscriptions area.
4.) Click onto get gold.
5.) There will be an option at the top for the free 1 month trial. Click that and follow the instructions.
You will need to enter a payment method as it sets up a automatic renewal once it runs out. The automatic renewal can be turned off though once you have the trial set up by finding the option within your subscription area (this can be done at any time).
If you have already redeemed an offer like this in the past, I'm not sure if you will be able to again but it's worth a try. The offer is also only available to those who do not currently have a gold account.