Contact customer service - many times by chatting with a customer service representative they will give you extra discounts to complete your purchase.
Set up discount email - to clean things up, set up an email specifically for collecting coupons and discounts without cluttering your personal email.
Enter multiple coupon codes - combine multiple coupon codes at checkout to score the biggest savings. Also referred to as stackable coupons; combine a sitewide coupon with a free shipping code.
Use multiple email addresses - sign up for stores email lists using a couple different email accounts. Stores will offer single use coupon codes, combine these single use coupon codes from multiple email accounts to maximize savings.
Use reward programs - check out such products as Swagbucks and Shopkick, these companies will give you special discounts and gifts for filling out surveys and shopping around.