When I said it was fine to leave your camera on auto when you're starting out (and later if that's what works for you!) this is why. Composition is more important. There are rules you can follow here, and breaking them can be good too. Composition is one of the most important differences between a good photo and a bad one. And with the right composition, sometimes a photo that isn't really of anything interesting can still be good.
Rule of Thirds
The Rule of Thirds is probably the most commonly used rule for composition, because it works. Take a simple landscape. Sky. Land. Divide them across the middle of the frame, and it looks dull. Divide them in thirds, and it looks much better. Doesn't matter if it's one-third sky or two-thirds - that just depends which bit is more interesting, or you want to draw attention to. But split them in thirds, and it just feels good.
Same applies to many other subjects. Put a person one-third of the way across the frame, and it usually looks better than having them in the middle. Get your subject's eyes at one-third from the top. Have that person walking along the street over the road from you one-third of the way into the frame.
Breaking the Rule of Thirds
Rules are made to be broken. Sometimes, thirds aren't right. A big, wide, empty landscape can look great when the frame is mostly sky, with just a bit of land at the bottom. It emphasises the huge sky, towering over the land. Portraits often look good with the subject right in the middle. A walking subject about to step out of the frame can make the viewer think about where they might be going, taking the story of the photo out of the frame.
These things can be unexpected, which can add some interest to a photo.
My advice would be to use the Rule of Thirds a lot. Learn it until it becomes natural. Then learn when to break it.
It's probably worth mentioning Instagram at this point. One app shouldn't really change general rules for composition, but I think Instagram has. It does allow other formats now, but for years, it was square-only. And square compositions do tend to favour central splits, or having the subject right in the middle. So it's become a more common thing to do.