Here are some tips:

• Read the recipe
• Assemble the ingredients
• Measure flour correctly—see the video: https://youtu.be/JFkwbuzthLU
• Stir dry ingredients together, no need to sift
• Butter and eggs should be room temperature, set them out 30-60 minutes prior to baking
• Use half butter half shortening for best results, margarine has too much water
• Why not margarine?

• In fact most "margarines" are not even margarine—look at the label, if it says "margarine" then it must be 80% oil, by law, if it only says vegetable oil spread or the brand name then it has much less oil and consequently too much water
• Why not all butter?
• Butter tends to melt more quickly than shortening, so using all butter will make your cookie spread out during bakingCream the butter and sugar for 3-5 minutes, until light and fluffy
• Use more white sugar if you want crisp cookies, more brown if you like chewy, keeping the total amount of sugar the same
• Use a cookie scoop to ensure cookies are all the same size
• Rotate the cookie sheets during baking. Top to bottom, spin the sheet around mid-cooking time
• Let the cookie sheets cool in between batches
• Problems?
• Flat cookies?

Your butter was too soft, it should just yield to pressure

You didn't use enough flour—measure correctly, watch this video : https://youtu.be/JFkwbuzthLU

Your cookie sheet was too hot—let them cool between batches

• Hard, crunchy cookies?

• Check out my video on facebook
• Practice, practice, practice!