I’ve been baking since I was a child and spent years working in restaurants. Over the years I’ve learned three easy tips for making better cookies:
1. Use dark brown sugar instead of light brown sugar for a richer taste;
2. Add a little (1/4 cup or so) extra flour than most recipes call for; and
3. Always refrigerate the cookie dough for at least 8 hours (or more) to keep cookies from baking down. I know people that refrigerate their cookie dough for 24-36 hours (although I must admit I don't have much willpower when it comes to cookie dough in my fridge!). This also allows the gluten to settle and allows the dry ingredients to have a chance to absorb the moist ingredients, which results in better flavors.