Be descriptive – a title that just says “Big Sale at Farmers” is much less useful than a title that says “Kids Wear 40% off Sale at Farmers Wellington Stores Only”
Don't be spammy – a title should be clear, concise, informative and unbiased, i.e. providing sufficient information to let other members to decide whether it is a good deal. Marketing speak and personal opinions create bias.
Mention if users need to Like on Facebook, Retweet on Twitter, or perform some other online task to acquire the deal.