I have been doing a couple of things differently with my cookies lately, and they've been turning out consistently better. So here are some tips for chocolate chip:
Soften your butter at room temperature rather than melting it in the microwave. If you need to pop it in the microwave for 10-15 seconds just to get it a little softer it seems to work fine, but going from frozen to melted in a minute (something I was doing) does not give you the best results. (With cookie bars this doesn't seem to matter as much. You can microwave your butter and the bars are fine.)
Add almost three cups of flour. Not quite 3, as I think that's too much, but closer to 3 c than 2 1/2. At 2 1/2 your cookies will probably not have enough and be too flat.
To spruce up your chocolate chip recipe, add M&M's, mini M&M's, or peanut butter chips to your regular semisweet chips.
Dough refrigerates well. I've been making a batch of dough, only baking one tray, and then doing another tray each day for the next several days. That way we have fresh, warm cookies whenever we want them instead of a huge batch sitting around getting stale on the counter. You can let the dough thaw on the counter for 15-30 minutes and it should be good to go. I roll my dough into balls with my hands to get a nice round cookie.
Pull the cookies out of the oven just before they look done to you, and let them finish baking for a few minutes on the cookie sheet.
Anyway, those are just some thoughts. It's a process, perfecting cookies, and a yummy one at that!
Click here for my chocolate chip cookie recipe. Happy baking!