Two of the most important tips my mom taught me are also extremely simple: 1. always read the recipe first and 2. always double check that you've added all the ingredients when you're done. I will admit I sometimes fail to do these things and when I do, I usually regret it. While there are plenty of dishes that can't really be saved if I've forgetten something, with a little improvisation so many can be. I have at least some chance of salvaging a recipe (particularly a baking recipe) if I catch an omission before the recipe hits the oven! It's also much easier to change recipes altogether if a thorough reading beforehand makes me realize I am missing an essential ingredient or that a particular step takes a lot of time I don't have (say chilling for several hours before baking.)
Now that I'm thinking about it, I don't think my mom specifically told me the importance of these things, but they are steps she always does herself, so I definitely learned by example!