Before you start baking, read completely through your recipe so you know what to expect. Get all your ingredients and measuring tools out as well. If everything is right in front of you, you won't be bouncing around the kitchen and you won't leave an ingredient out. Also, you won't get half way through a recipe and realize you are completely out of vanilla extract and have to run to the store.
When you are done mixing everything together, read through your ingredient list and recipe AGAIN. This way you will know if you skipped a step or left out an ingredient.
Use measuring tools! Baking is a precise art. It's chemistry. You need to use the measurements specified in the recipe, unless it's something like nuts or chocolate chips where you might like more or less. But as for the basics, follow the measurements and be exact.
Use tools you like. My big green bowl is a great mixing bowl and I get happy just pulling it off the shelf. My measuring cups and spoons, and my wooden mixing spoon, even my rubber spatula, are all specially chosen for the way they look and feel.
"A thing of beauty is a joy forever."- Mary Poppins
Invest in a good cookie scoop. 1-1/2" is a good size. Your cookies will all be the same size and shape.
Use real butter, NOT margarine. It is not better for you and hey, you're BAKING, why worry about that anyway? Butter tastes better and bakes up better. I also use recipes that call for shortening. If you are anti-shortening, might as well leave right now. This is not a health-food baking blog! Crisco makes the texture of baked goods soft and chewy. If you substitute butter for Crisco, the recipe will NOT turn out the same. Your cookies will be flat and crispy.
Use REAL vanilla. Not that imitation
Use REAL chocolate chips. Not that imitation
Always have oranges and lemons on hand, and a good zester.
It's a good idea to bring eggs to room temp before you bake. Cold eggs don't incorporate into the batter as well. If you don't have time to let your eggs sit for a bit, just put them in a bowl of very warm water for about a minute.
When measuring flour, use a spoon to lightly fill your measuring cup all the way, then use the flat side of a knife to scrape off the excess.
When measuring brown sugar, always pack it firmly with a spoon.
Don't overcrowd your oven. Put one cookie sheet in at a time and just be patient. If you overcrowd your oven, your cookies will bake unevenly.
The key to delicious cookies is to NOT OVERCOOK them!! Under-cook them a little. They will cook up a little more after you take them out of the oven and let them cool a bit on the cookie sheet. Trust me on this.
Invest in cooling racks. Truly, it will make your life easier. Paper towels do not cut it.
The most important tip? Have fun and bake often!!