There is no substitution for butter in cookies. I always use real butter. You should make sure your butter is not stale and has absorbed smells from the refrigerator. Old stale butter will make your cookies taste horrible.
Another item not to skimp on is pure vanilla extract. Never use imitation vanilla. Try using a good brand of pure vanilla extract such as Nielsen-Massey Madagascar Bourbon Pure Vanilla Extract for Baking and Cooking. It will make a difference in your cookie.
Room temperature eggs for baking helps the eggs to blend in your batter better and more evenly. Cold eggs could make your batter lumpy and require the cookies to bake a little longer. Normally, it will take 30 minutes for eggs to reach room temperature.
There are a number of good reasons to use parchment paper. The important one is the parchment paper helps to bake the cookies evenly. Another important tip is the non-stick quality of parchment paper will help prevent the cookies from cracking or breaking when lifting them off the sheet.
For more information and other quick tips, please check out my blog.