Learn how to set up and build an email list for your business website.
Your free giveaway needs to be a valuable ebook/report/software program/etc. that will encourage people to give their contact information to you and join your list in return for it.
Best, most effective free giveaways are those that address a need or want of your target market- research online via competitors’ websites and online forums that cater to your niche to find out what will make the best free giveaways.