Don't over-bake them!
It sounds simple enough--but most cookies are over-baked. Then they're dry and hard.
There's a simple way to check your cookies. When you take your cookies from the oven, put the first one on the rack, lift the rack, and look at the bottom. It should be gold.
If it's brown, it's over-baked.
And seconds count. Use a digital timer like the one on your microwave. My favorite cookies in our oven are done in 8 minutes an 45 seconds. Nine minutes is too long.