Step 1: Overview
With this instructional I hope to teach you a few simple tricks to kick up your cooking from tasty to insane.
Step 2: Know Your Herbs
Use fresh herbs where possible. Some herbs, you have no choice. Finding fresh mace or marjoram will be cost prohibitive and difficult. Fresh basil, oregano, rosemary, parsley, or garlic? less. Never skimp on the herbs, fresh is infinitely better than dried.
A good rule of thumb for fresh herbs is use twice as much of the fresh stuff as you do the dried, and try to only cut them once. A good fine chop is important, but if you over-chop them and go crazy with the knife you bruise them and lose some of that flavor.
One of the main reasons you REALLY want to know what your herbs are and how they interact is, in a nutshell, versatility. Sometimes swapping out a bit of sweet paprika for some half sharp will add new dimensions to a dish, and if you don't know what the difference is you'd never think to do so, and your cooking lacks a bit of refinement and dimension. A great chef experiments, constantly. I'll get to that later.
Aside from that, if you know how the herbs interact well enough, you can deconstruct someone else's recipes and pull what's useful out of them. Make them your own.
Step 3: Simplicity
Always remember the golden rule. You can always add more, but with most things you can never remove.
A great example of simplicity in action is the pizza margherita. Pizza is the american meal, anymore. Americans eat, per person, an average of 23 pounds of pizza per year. When you consider that a true pizza margherita is just dough, plain sauce, basil leaves, and cheese? Sometimes the best food is the least complex.
Aside from that, well, let's get to the root of cooking. You're not cooking the herbs (usually), you're cooking the meat. Potatoes. Vegetables. Whatever. If you overdo it with seasonings and spices, you're no longer tasting the thing you set out to cook, you're tasting the huge combination of spices. To cook a thing is to, in a nutshell, pay homage to it. A dish is a play, and the food is the star. Cluttering up the scenery needlessly is pointless. Just let the star of the dish do what it does, and set the rest of the stage to accentuate it's positive points.
Step 4: Read
A great chef can look in the kitchen, see 2 eggs, some milk, a bit of butter, a tiny bit of flour, and a meager stash of herbs, and then fill your ear for the next 20 minutes with all of the things he can make from them.
Also, take nothing you read in any cook book as useless. Even if you hate every single ingredient in the meal, you still might be able to steal one of the preparation processes for some of the ingredients and use them in your other recipes. A good example of this is, for me, root vegetables. I hate most of them. However, anything you can do with most of them, you can do to a carrot or a potato. Most foods work this way in one way or another.
Step 5: Presentation Is Key
Good food is aromatic and flavorful. Great food is edible art. This doesn't mean you have to go all nouvelle cuisine on the plate, and make it look like Dali sneezed on it, but at the same time you don't want to serve a huge mass of unrecognizable gunk. That gunk could be the tastiest thing on the planet, but if you don't present it properly it loses all of it's impact.
Step 6: Find a Signature
Above that, learn from styles, and master them one at at a time. Learn your favorite style first, and get a strong working grasp of how the cuisine works. Like italian? Make a great marinara. Learn to make pesto. Make some manicotti. Master the basics, then move on to something else.
Truly great food is a puzzle. If you master all of the pieces of one style, you can mix and match them to make unique creations.
Personally, I'm a master of the cream sauce. It's mostly my french, cajun, and italian cooking style, but I can make a cream sauce out of just about anything. Finding a general category like that, and mastering it's intricacies, will increase your skill dramatically.
Step 7: Experiment
Try new foods. Take no food as bad, offhand. Even the worst cooks can sometimes come out with a flavor combo or trick you'd never think of, and any ingredient can taste good in the proper context.
An addendum to this, because a good point was made in the comment, is that I should probably expand on this concept. When I said know your herbs, i was dead serious. Know what each of them tastes like, what they mix well with, and what they contrast. Sometimes, if you're cooking, You'll taste your dish and notice it's lacking something, or you feel the urge to take it in a new direction this time. If you know your herbs, you can toss something extra, just to modify the flavor slightly. I suggest doing this on your own free time, but the best dishes come from a cook deciding to try a pinch of cilantro in his pesto, or things like that.
Following recipes, even your own, as gospel takes the art out of food. In your free time, experiment. If you think you're on to something, toss it to a friend and have them give input.
Cooking has very few concrete rules about what should taste good. Explore the varying combinations and you'll become a better chef, by default.
A caveat to this, however, is that you'll want to experiment in a style you've got a good working grasp of. My technique of doing this is the spice of the month. I pick up a spice I've never touched before, and smell it. Taste it. cook something simple, and let that herb be the star. Look up a few recipes that contain it, so I can feel how it should portion into a dish.This way you'll understand what other flavors mesh well with it.
Another caveat to this is if you don't know your spices, completely, to know exactly what they will do when mixed, don't make anyone else eat your experiments. That's just rude.
Step 8: Wrapup
Following recipes doesn't make you a cook. A robot could do that. Innovate, and explore.