Also if you're new to baking, it's the one type of cooking I've found where winging it doesn't work well! Measuring precisely, and following the directions exactly is almost always required. Most common mistakes I see: measuring dry ingredients with liquid measuring cups, using table spoons rather than measuring spoons, using baking powder instead of soda and vice-versa or skipping one when both are called for, skimping on butter or oil, substituting butter for oil (sometimes ok, try the recipe as directed first). The biggest mistake (and most common)? Filling measuring cups by pouring or scooping in with a spoon rather than the "dip and level" method.
Dip your measuring cup in the the dry ingredient bin, completely overfilling it, and then using the flat side of a knife (or a flat baking spatula), swipe off the excess. It's easier to do this with good quality measuring cups and spoons - stainless steel with straight sides and no lip. I have some basic ones too that don't have a clean top edge, and unfortunately I've found they don't give me a consistent measure.
If a recipe calls for sifting, some need sifting before you add the dry ingredients. Some recipes call for pre-sifting and then sifting the ingredients together, and some call for triple sifting. Measure before you sift either way, and don't skip it. I have a small spin sifter I've owned forever; an inexpensive tool that comes in handy especially for pancakes and cakes. And though I'm sure there are substitutes, if it calls for cake flour, use cake flour.
Lastly, I make a recipe first using all of the directions, and then see what I can get away with. For example, cookies and muffins are often more forgiving than cakes, but as you've found, not always. I took a banana bread recipe, and over time added bran, whole wheat flour (50-50 with white flour), applesauce instead of 1/2 the oil, shredded carrots, shredded zucchini, and half of the banana to make "morning muffins," which I then froze in a huge baggie for grab & go or packing in lunches for my kids. Had I not tried the primary recipe first, then made subtle changes (like adding the nutmeg, adding more veggies, reducing the banana) one by one, I wouldn't have known what worked and what didn't. Adding nuts, for example, didn't freeze as well.
Enjoy!