I know some shops often offer seasonal discounts, but it always differs depending on the industry or how close/far it is from important holidays or events. How do you know which ones are about to offer discounts?
Here, where I live, there is often a discount on products shortly before the end of the month. That's basically, when most people have spent their monthly allowance, and are awaiting their next paycheck. So, if, for example, you want to buy a new washing machine, you will find that the price drops up to 35% just before the end of the month, and then goes right up again on the 1st of the next month.
Over here, the Christmas season is the biggest shopping season here. You need not look far because there are flea markets almost anywhere. And the sales are real sales down to less than 50% off the regular price and sometimes much lower. But in malls are the big events particularly the so called midnight sale. It is fun to experience shopping until midnight, searching for discounted items and successfully getting what you want.
I usually just sign up for newsletters, and also just by intuition after shopping at the same sites for years you get to develop a feel of when they usually start their deals and how frequently they put out promos. I have a favorite online store here that I've bought from a lot and studied in the past few years so I know their maximum and minimum amounts of discounts, and I know if the discount is worth it or if it's better to wait a while for the bigger ones. I just bought an item today, for example, and I was about to buy it yesterday but remembered that I should wait until the weekend so they would put up some vouchers and they did so I got to save a little just by waiting a while longer.
When I find a shop or online business I like I sign up for their newsletters and up-dates. I get from amazon.com just exactly when they'll have their cyber Monday sales and other shops let me know everything about their sales and specials. It's wonderful for I get advance notice and know of their next sales!