Fundamentally, cameras are terrible at picking a decent A/S/P values for scenes ( though they have much improved ) because the cameras cannot correctly analyze what important vs. unimportnat portions of a scene.
So if you are using your DSLR or mirrorless for something other than phone-like snapshots you should give your camera a hand, and that hand is semi manual mode ( the reason why it is a semi-manual mode is because you are still going to rely on/tweak what camera thinks you should do ). To achieve the technically best results ( not artistic, but just technical ), you should remember:
1. Tell the camera what to measure - if you are not looking at producing phone-like snapshots, switch the metering mode to spot metering or its equivalent. Use the crosshair/dot to point at the spot you want to come out correctly exposed. Just by doing this single little thing you would absolutely improve the automatic exposure. Compared to what you can achieve by switching the point on camera is pretty amazing.
2. Look at what the camera tells you its settings are and use that as the base.
3. Unless you really know what you doing you ALWAYS want to shoot at the lowest ISO, which is why letting a camera set the ISO is pretty much never a good idea. What looks fine on a phone or on a camera display will look pretty icky on a large screen or printed. Most of the cameras now have ability to lock the max ISO. Use it. You should never go above ISO 800 without unlocking it.
4. The rule of the thumb is that shutter speed above 1/60 probably will introduce blur if the subjects are moving. If you are just starting you should keep the shutter at 1/60s of above.
Look at what the camera tells you about the exposure. If it is too low, first drop the ISO to the minimum your camera can do. Still too low? Start decreasing your shutter speed to 1/60s. Still too low? Start opening your lens by increasing the <number> on the f/<number> ( there are side effects in this and eventually you would recognize that for some scenes you want to stop at not the lowest <number> but for the exposure part it is not really relevant ). Still too low? Start increasing the ISO until you hit what the camera thinks is a good exposure.
Now the critical part: ( because the camera even now will probably be not quite right ). Take a shot. Go to histogram. Make sure that the histogram's breakdown matches your view of the scene. If it does, great! If it does not ( histogram of the image indicates scene is dark but the scene is light or reverse ) tweak the exposure ( using the same order or reverse depending on if you want to increase or decrease the exposure ) until the histogram of the next photo makes sense.
P.S. Remember, human eye gets a lot more light in compared to the lens that you are using. If you want to get a ballpark idea of how much light gets into a lens, squint