When you're running a promotion or a sale, you should be have a clear goal.
Perhaps your goal is to get new customers. Then you might want to incentivize the first order or a mailing list signup.
Or perhaps you want to clear out inventory. Then you might want to deeply discount some products or message around stocking up.
Or perhaps you just need an injection of profit. Then you might feature your most profitable products and add bonus offers while avoiding discounting entirely.
If you don't know what your goal is, you might run into unintended consequences and make decisions that work against you. Or even worse, you might be mimicking what a competitor does without knowing their goals and end up in a bad state after the promotion.
Tying your goal to a metric is a great way to measure your goal's success. It could be something like "I want my AOV for new customers this month to increase to $80" or "these dozen products should have their inventory reduced to below 20".
Whatever sale you do, make sure to track your long-term metrics for customers who participated. You want to avoid training customers to wait for promotions, that's a sign of bad customer behavior.
You can use cohorts in Repeat Customer Insights to track behavior from one month to the next. Or the Customer Grid History to compare shifts in your customer segments over time.