As a competitor have you been to any tournaments? What proved difficult for you there?
What you can always work on, by yourself, is tech skill. There is no skill ceiling, so keep grinding movement, ledge options, SHFFLs etc.
If you have 20XX hack pack then practice downthrow tech chasing on reaction.
Read MU articles and think about MU. What works and what does not work. What do certain people do in certain scenarios (look up videos of tournament matches). Take notes.
Talk to your friends about smash. Study frame data. Search for more terminology. Teach what you discover to your training partners. Tell them what they did wrong. Ask what you can do better. Theory craft together.
And play some friendlies.
Write down a list of things you know you did wrong. Keep the list visual to you as you play more matches. Remind yourself of those things.
https://www.reddit.com/r/SSBM/comments/2rnvkv/list_of_common_noob_habits_you_should_all_try_to/
Look at this list.
Work towards crossing EVERYTHING off that list.