The thing is you can grind tech skill all day and be the most technical player at home when you're facing computers, but if you don't face human opponents then you will probably lock up when you do and on top of that you will not know how to utilize the techniques in a real game.
Now, there are things you can do by yourself. Number one is grind tech skill. You might be thinking that's silly because of what I just said, but you do need to know how to do tech if you are going to try and implement it. Number two is to work on your movement, so like look up videos of top players and try to emulate how they move around the stage. Like I said before, when you first start playing against real people this won't help much at all but the foundation will serve you later on.
I would actually try to not focus on comboing computers that much because you will learn very bad habits since you don't know how people play and react. Do it a little bit so you know how your moves work and how you can potentially link them together, but don't get too into it.
You really need to find people to play. There are many ways to do this but it kinda depends on your age and where you live and your transportation availability, so I'm not sure what to suggest. If you're still in school you can try to get your friends interested and then learn with them, or start a smash club to try to attract any players in your area or new players who want to learn. It's summer now, so maybe that's hard but it does leave you more availabl to travel to play with people. If you're in college finding people should be no issue (with the exception of it being summer). If you're out of college join a smash FaceBook group in your area since you should be free to travel places.