The easiest way to learn the game is probably by doing good things randomly and then adjusting in a way that should work. You learn to do good things through a cycle of analysis, practice and usage.
Maybe that sounds too vague?
Here's an example:
1.) Take a MU. Sheik vs Marth for now.
2.) Take a situation. Sheik hanging on the ledge of BF, Marth below the inner edge of a side platform. Both at 15%. Etc.
3.) Look at the situation. Try to come up with 3 or 4 or 5 good options that end up giving you something better than currently and cannot be covered by the same actions from the opponent. This is where general game knowledge and watching top players comes in.
4.) Once you find those options (in this case let's say they're shinostall, ledgedash far boost grab, ledgedash barely on stage, double jump barely on stage, double jump stall) practice them at home.
5.) Apply them when playing someone. Don't focus too much on winning the game, but to seeing what happens after you pick an option. If something tends to get you killed stop doing it in that situation. If you fail at doing something grind it out. If something works well use more of it until the opponent shows he can deal with it and then choose something else.
6.) Learn some new situation or go back to the drawing board if you're not happy with your results.
I suggest drawing up charts of different things like stage position and ranges to simplify them and not getting a one track mind. Think about the risk-reward ratios of options too, like an ftilt is super op if the opponent can't/doesn't CC, but if he can it's dangerous.
This game is hard, especially when starting out, since it's so fast and there are so many things you need to take into account. So you kind of just have to learn it by heart by playing, practicing and thinking a lot. And you'll get rekt a lot while doing that and that's ok.
