I think it depends on what you are wanting to giveaway. If you are crafty and are wanting to giveaway something that you have made then get involved in blogging parties such as the ones held by SITS (Secret is in the sauce) and 5 Minutes 4 Mom to build traffic for your contest, thus getting more traffic and hopefully more readers for your blog too. If you are wanting to do a sponsored giveaway from a company then you really need to build your readership or have a blog that is specialized to a particular topic.
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