Always use parchment paper when you bake. I use it to line everything. It keeps things from sticking and prevents the bottoms from burning by placing a barrier between the metal and the delicate cookie. Besides this incredible feat, parchment paper prolongs the luster and condition of your pans because you will not be scouring crusty baked goods off and scratching them. You can buy parchment paper in rolls on the bottom shelf at most grocery stores in the aisle with foils and plastic bags.
I prefer to get mine in sheets so I do not have to fuss with the curling of the rolled paper. You can get it in precut sheets at Country Kitchen Sweetart, 4621 Speedway Drive, or online at KingArthurFlour.com. Incidentally, you can just use the same sheet for the whole batch of cookies.
Some cooks like the Silpat, a rubberized floppy mat made in France and available at Williams Sonoma, Bed, Bath and Beyond, and Crate and Barrel. I like it too, but I do not like washing it and do not like the way it looks after it has been used a lot. There is nothing wrong with it, but it just gets dark, grungy and kind of sticky. They are pretty pricey, but the upside is a Silpat will last forever and is easy to store.
The other thing that will affect your baking is the temperature of your oven. A 350-degree oven is a moderate oven and is the most called for in baking. Many things are also 325. If you try to rush it and turn up the heat, it is just going to bake too fast in the wrong places. Remember to keep an eye on those cookies!
Many ovens are actually off caliber, and serious cooks often hang a thermometer in their oven just to be exact. I don't do this; I just keep my eye on the things I am making.
At Le Cordon Bleu, the chefs are maniacal about the placement of our cookies on the trays before putting them in the oven. You do not need to be this obsessed, but do not crowd them. Make sure each one has space around it so it can get heat on all sides. Better to bake one extra pan than ruin the hard work you have done.
Q. I want to upgrade my cookie sheets. Advice?
A. It is better to get two good cookies sheets than four bad ones. I love the Calphalon sheets because they distribute heat so evenly. They do not warp or rust. Because they are so well made they are very easy to clean and will last you for decades. I also like Williams Sonoma GoldTouch non-stick cookie sheets. It is not necessary to get non-stick if you use parchment paper when you bake. But they sure are easy to clean!
If you invest in a pricier pan, get one with sides, really called a sheet pan. This way you can use it for a myriad of things. I use mine for cookies, sheet cakes, roasting vegetables, roasting chicken breasts, carrying things — you get it. Also, if I am working fast, I do not want to take the chance of my food whizzing off a non-sided pan!