Practice is seriously the main thing, you can't get good without playing the game against humans a lot.
The tips I usually give for people starting out in the tournament scene is to just tell them about the fundamentals of the game. There are 5 fundamentals which apply to every character:
1.
Spacing: It's so important that you control the space because it is a huge factor of winning - in general the person who spaces better will win.
2.
Tech Skill: This is something you can practise at home, it's pretty much making sure you're fluent with all of your character's moves, combos and ATs and can perform them consistently in high pressure situations.
3.
Matchups: You gotta know them. If you've never played against ICs before you're gonna get wrecked because it's a matchup you have to play very different in for most characters. Watch videos of the top players of the matchup and see what they do to overcome it.
4.
Stages: You gotta know how to play on these as well, since in Smash the stage is a big factor on who gets the advantage in a matchup. If you don't know the mechanics of all the legal counterpicks in brawl you're gonna get a big surprise when playing on Frigate Orpheon and not jumping when the stage flips, only to find that you're stuck underneath the bottom unable to get back up (unless you're playing metaknight).
5.
Mindgames: This can only be developed through practising and playing with other humans a lot. Being able to outwit and crush the opponent's mind is a big asset since it can cause them to question themselves during a match, something they do not want to be doing.
Some things to think about, hope you found it useful.
