Most stores have a discount of 20% off or more to start the sale. I price about 90% of the merchandise to start the sale with a discount of 13% off. My best sale did over $150,000 with this discount resulting in $10,500 additional dollars in their bank account by using 13% off instead of 20%. The key is pricing the other 10% with additional markdowns. I discount mainly clearance and out of season items 50% off.
I have a few things 33% off and the rest 22% off to start. You must have some good merchandise with additional discounts.
For example, Christmas items would be 50% off unless it is fall. For hardware stores, I always start Paint & Stain and Furnace Filters 22% off and Hillman Nuts, Bolts, Washers, and Screws 50% off. These are excellent items to give a good perception about your pricing. Do not take an item you already have a discount and make the price higher during the sale. You risk a severe backlash on pricing.
Also, I had conducted two sales where the store owner raise prices a few months before the sale started. In both cases, the sale started lower, lasted longer, and the total return was among the lowest of all the sales I have done.
Normally, I change prices 4-7 days after the sale starts and weekly after that. Once most items are ½ off I keep prices for 10-14 days at 50% off. Some sales, I do need to adjust this based on the customer traffic. My largest discount is 80% off at the end of the sale. At the same time, I put prices on entire 3 and 4-foot sections to sell merchandise. Sometimes, you can get the customer to make an offer, but normally they do not.