First Day has a strong range of percentage discounts running right now, led by the 60% off deal that also includes free shipping and a free gift when you spend over $75. This is the best offer available for anyone willing to hit that spend threshold.
For smaller baskets under $75, your best option depends on how much you're spending. If you're buying up to $35 worth of items, the 10% off your order discount will give you a modest saving of around $3.50. For baskets between $35 and $75, you'll want to compare the 36% off and 40% off options—the 40% off deal will save you more money, so choose that one. At that spend level, the 40% off deal could save you $30 or more depending on your exact total.
Once your basket reaches $75 or above, the 60% off offer becomes your target. This deal combines the steep 60% discount with free shipping and a free gift, making it by far the strongest deal available. Even if you're just hitting $75, you'll save around $45 on top of getting free shipping and a bonus item. If you're spending $100, you're looking at savings of around $60 before the added value of free shipping and the gift.
If you're shopping from the Back-to-School Sale section of the site, the dedicated sale offer giving you up to 52% off sale products might be worth checking in your cart against the sitewide deals, though the 60% off deal at $75 and above will almost certainly beat it for savings.
Only one offer applies at checkout, so work out what your basket total is before you shop and compare the available options. Add items up to see which discount tier saves you the most money, then apply that deal at payment.