Ask for gift receipts for all of your gift purchases and attach them to the product or package right away. Retailers have clamped down on returns this year and that receipt is likely to be required for an exchange or return at the price you paid. Keep your own receipts, too—if something that you've purchased goes on sale, you can generally get a price adjustment up to two weeks after you bought it.
Be careful when ordering from websites without storefronts—many don't take returns at all.
Go easy on trinkets and stocking stuffers. They add up fast and are minimally appreciated. That goes for special gift bags and wrapping products, too.
One of my favorite gifts to give is a bulb garden in a special basket or box. I get consistently great feedback on that gift.
What about timing? Is it better to buy early or late?
It depends on the exclusivity of the gift. If there's something that's special or particular that you want somebody to have, don't wait too long. Generally speaking, clothes go on sale early and they'll become more reduced as the season progresses, electronics are best to buy during a promotion, toys typically don't go on sale until right before Christmas. Luxury items are best bought during early promotions—they'll sell out before clearance this year.
Any final advice?
Make a list. It sounds so Santa Claus-ish, but organization reduces stress and keeps you on budget.
Don't strive for perfection. Calculate the time and emotional cost of excessive shopping, baking, wrapping, and decorating against time spent enjoying the season and the important people in your life.