By mid-August, the real summer sales are basically over, so if you're waiting for the next big discounts, you're probably looking at September or thereabouts. If you need things by the end of August, check the prices now because they're unlikely to drop suddenly. That said, Amazon runs promotions on different items almost every day, so it's worth checking regularly if you're not in a rush.
The trick is to use the app or website to add items you need to your wishlist, then check the price chart (when there is one) to see if the current price is already low compared to recent weeks. Don't blindly believe the percentage discounts you see in red: sometimes Amazon inflates the starting price to make the discount look bigger. Another thing a lot of people miss is that during real "sales," the best items sell out quickly, so if you see something that's a good deal, don't wait until the next day.
If you want to be systematic about it, you can try turning on price notifications for specific products, so you get an alert when they drop. But honestly, if it's not urgent, waiting until mid-September makes more sense because discounts come back strong then.