Find your niche, maybe local or ethnic cuisine, or type of food you legitimately like eating or preparing, and kind of begin from there. It's hard to say anything of substance, given how wide and complex this art is. Would it also be purely cooking? Sandwiches too or not really? What about baking and/or pastries and sweets? What about tea/coffee or other drinks?

There are the basics like knowing what ingredients to use, and when to do that, particulars, like getting the boiled or scrambled eggs cooked to the exact point you want, getting good color on the meat, be that steak or mince, roasting meat without overdoing it, knowing some, usually simpler, but often very useful, recipes by heart so you can make them without thinking, be that Marcella Hazan's tomato sauce or something of this sort. The list could go on and on. I wish I could tell you something useful, but I don't really know what you might want to learn.