1. Invest in a decent, sharp knife. A knife is the cook's main tool in the kitchen - there are loads to choose from in the shops ranging from a tenner all the way up to celebrity-endorsed ones topping hundreds of pounds. A good knife should be well balanced, and made of a fairly hard steel that will take regular sharpening. If you watch a butcher, they'll be sharpening their knives between every task, and letting the knife do the work. Sharpening with a whetstone is best I think, imagine that you're shaving very thin slices from the stone towards you and away from you, and you'll have a razor-sharp knife in about six moves
2. Use your senses. Cooking is a sensory experience, so look at the ingredients as you cook them, taste as you go, smell the food, listen to it cooking - a buzzword around at the moment is 'mindfulness' - be mindful as you cook (always makes me think of Jedi training!) A big influence on my cooking has been the idea known for centuries in the near and Far East of balance between flavours; sweet, sour, salty, sharp and the new kid on the block, at least in Western cooking, of Umami - food rich in this are mushrooms, soy, anchovies, parmesan cheese and many others. Also important to me is the texture of food - some foods I don't like simply because I don't like the texture - bread & butter pudding or baked beans - but a dish should have a mix of textures, created either by the cooking e.g. frying meat before you add it to a dish (this is done not in order to 'seal in the juices' which is a myth, but to cause something called the Maillard effect, which caramelizes the natural sugars in the meat to bring out the flavour and to create another texture in the mouth when you eat), or by the combination of the ingredients.
3. Let the food cook. I once watched a TV chef giving advice on cooking steaks - he said quite simply something along the lines of - lay the steak in a hot pan and leave it alone! - no lifting or prodding or stirring until halfway through when you turn the steak over. Of course you need to stir food to stop it burning, or to avoid lumpy sauces and that is correct, but I've seen so many cooks prolong the cooking process by lifting food off the heat to see if it's cooked, or constantly opening the oven doors and so on. Use a timer, use your eyes and nose to tell when things are done but let the food cook.
4. Make time to cook from scratch. I work on average ten or eleven hour days, which isn't that much in catering, and many people work much longer, and on occasions at home we'll say, 'let's get a takeaway', which is only right, but mostly at home we'll cook from scratch - there is something very satisfying and therapeutic about measuring, preparing and combining ingredients to come up with a dish that's better than one you could buy from a shop. I'm not suggesting that everything needs to be home-made - puff pastry for one thing is much easier to buy than make and just as good, but if you take the time to make things like sauces from scratch, and to find out what works or not, and what you like or not, then you're bound to become a better cook. And it's generally cheaper and better for you!
5. Be creative! I'm not a proponent of mixing thousands of ingredients or pairing weird and wonderful flavours as seems to be the current trend, if television cookery programs are to be believed - strawberries and fish, or scallops, ginger and black pudding spring to mind - but get to know what works well or not. Recently I made a rhubarb cake: rhubarb is coming to the end of its season now, and gooseberries are coming on, so I'll be making gooseberry cake - it can be as simple as that. If you don't like one ingredient, or can't get hold of something, use something else that fits.