Mostly trial-and-error, don't think I've used any books, though I'm sure I've gotten ideas from online recipes. My staples are either "some kind of soup" or "some kind of stir-fry on rice". Mostly vegetarian, not really strictly, but meat goes bad quickly so I tend not to have it. These two styles of cooking are also nice because the ingredient list is flexible. Almost any combination "works", it's just a matter of figuring out which combinations you like. The stir-fry-on-rice is only convenient if you have a rice cooker, though. Making rice on the stove without burning it is a hassle. Soups are mostly unattended cooking once you figure out what stove setting is "simmer" for the size of pot you're using (i.e. doesn't cool off so much it stops bubbling entirely, but also doesn't boil over). Depends or your taste, but for me even quite simple soups can be nice, e.g. boil some water and add lentils, potatoes, onions, salt, and some kind of spices (peppercorns, bay leaf, garlic, maybe a hot pepper). I usually serve with a drizzle of olive oil & vinegar and a side of nice bakery bread (I draw the line at baking!). Easiest way to make the same recipe non-vegetarian is probably to add in some chopped sausage or ham. Soup also works well with making extra amounts to refrigerate for leftovers, because unlike many foods it actually gets better on the 2nd day (ingredients' flavors mix more).

I also have a quick-and-dirty burrito I like to make: dice onions and optionally hot peppers, tomatoes, etc., sautee for a few minutes, add a can of canned beans and mix for a few more minutes, put into a tortilla with sour cream, done. It's not carnitas from a good taqueria, but I live in the UK, so the bar for outdoing a takeaway burrito is not that high. ;-)

A nice side dish, or a main dish for some people, are "greens" of various kinds (turnip, collard, dandelion, etc., can also use kale). Just put in a pot with a small amount of water, put on the lid, and steam until they're soft (shouldn't take more than 15 mins). Add olive oil, vinegar, and salt. Can make it into a more hearty main dish by adding in some chopped ham or bacon (with bacon, add it first and cook a few minutes to make sure it's fully cooked).

There's also "all-day breakfast", if you want to follow the current restaurant trend. ;-) Frying up eggs & bacon & toast takes almost no time at all!

I recommend Mark Bitman's "how to cook anything". He pares his recipes down to the minimum ingredients.