I think I need to get a better understanding of such mechanics too.
Yup person above is bang on.
I think the best thing to learn to master is:
1. Using your shield and options out of shield. You can be like 80% of people with just knowing this, how to edge guard, as a lot of people don't know how to do it.
2. If you pick a character than can do it, someone who can off stage destroy someone is very useful; this includes people with multiple jumps like inkling, and people with spikes, like mario
3. Learn to short hop and short hop neutral air. It basically just gives you another attack on the ground against bigger targets, is really nice for edge guarding.
4. Pick one character and master him
5. when you jump, at the peak of ur jump press down, it makes them fall way quicker, gives you a lot more options going back to ground, and gives the illusion you are faster than you are; making heavier characters like ganondorf scary.
I play around with Ganondorf, Bowser and if I need to get serious Inkling/Yoshi.
Gandondorf/Bowser suck compared to the top characters but they are brilliant to learn the game with because you have a much bigger margin for error due to their weight, and they don't rely on combos. Specifically Ganondorf basically has no complex combos, its more "I hit you for 20% then move away". You can also kill people at like 60% with his forward smash which isn't hard to pull off if you can predict someones moves. And what i love best about him is his netural forward air is a KILL MOVE!!! at low percentages like 80-90%.
Also if you can master Ganondorf's mobility, then everyone else feels like a dream in comparison.