1. Measure Carefully
Any sugar cookie recipe is a delicate proportional balance of fat, sugar and flour, so be sure to measure your ingredients carefully in order to get the desired finished texture (crisp, chewy, delicate, melting, etc).
2. Mind Your Butter!
A key step in making sugar cookies is the creaming of butter and sugar. If the butter is too soft, your cookies will be greasy, and if it is too cold, they'll seem like lead weights. It is important to start with evenly softened butter, and the only way to do this properly is to take it out of the refrigerator and, uh, wait. Always soften butter in a temperate environment until it yields gently to pressure; if you want to hasten the process a bit, cut the butter into even sized pieces and spread them out. This is not the time to attempt any wacky moves in the microwave or on the stovetop. If your recipe requires shortening, make sure it is ultra-fresh and stored in a cool, dry place to maintain the proper consistency.
3. Keep Flavorings Simple and of the Highest Quality
Sugar cookies are, by nature, an example of sublime simplicity. Vanilla is classic, and some freshly grated lemon or orange zest provides a nice contrast. Anything beyond that, and it becomes a different cookie.
4. Roll and Cut in a Dough-Friendly Environment
This means as far away from the screaming hot oven as possible. After chilling your dough, divide it into three or four pieces. Soften it just until you can press it slightly with your rolling pin; the dough should still be cool to the touch while you are rolling. Work in an assembly line, keeping the other pieces of dough chilled. Keep your rolling surface well dusted with flour—but not too much—and move the dough around to prevent it from sticking. Cut your cookies closely as possible to minimize the amount of scraps, since the dough will become tougher each time your re-roll it.
5. Move Your Baking Sheets
Rotate your baking sheets 180 degrees, halfway through the baking time. Baking on the center rack is best, but if you are using multiple oven racks, switch the position of the sheets, moving top to bottom, bottom to top. Both steps will help the cookies brown evenly and help to prevent over-browned edges.