Eventually this will be a long list of things you can do, and things to avoid. (Trust me I've done them all!). Most of these will no doubt be for people with less experiance than myself. If you know better than to do any of these, more power to you but get over your ego some people learn the hard way.
So until I can organize my thoughts here are some things that come to mind.
When working with sauces or drippings, don't add salt or salted products until the end. You want control over the flavor and sauces that are doing to be reducing only get saltier.
Don't be afraid to get your hands dirty.
Keep your knife handle clean and dry. It WILL slip and cut you.
When deboning or carving meat, cut through the joint. It will be easier on your and your knife.
De-gill your mushrooms before you put them in a white sauce.
Always stir all the way to the bottom of your pan when cooking.
A metal handle will often be hot when a pan is on a stove.
DON'T EVER LEAVE YOUR KNIFE IN THE SINK!!
A cold plate will suck the life out of your food, ever wonder what the plate warmer setting is for on your dish washer?
A real chef doesn't need a bunch of tools to do his work for him.
Recipies are not written in stone.
If you don't know, ask.
Get your stuff and see if you have it all before you start cooking something. Especially if you are baking.
KNow how to work everything before you use something you've never used before.
Always pay attention in a kitchen.