That's a hard one for me to answer with those questions. I don't have "sales" as such. We have a "special offer" every month with our newsmailer. And it's always random offers (ie.an extra mat free, or non-glare glass at regular price etc). That way customers don't expect a certain thing at a certain time. The last thing you want is for everyone to save up their framing for the "Big Sale". As for coupons I might give a customer (or the mailing list) a "special gift" of 10%-20% off on certain things, but not just "coupons to the masses". I think you should reward your existing customers.
I believe the retail industry has shot themselves in the foot with Christmas Sales. Now, the consumer expects them, and won't begin shopping until the obligatory "sale" begins. I even know of some folks that have their "Christmas" after Christmas in order to take advantage of sales.
I guess this falls under the catagory of "don't get me started!"
Betty