The first thing I would recommend is for you to develop your tech skill. Simple shffl aerials. The start working on your dash dance game(assuming you play marth). Watch Dr.PP or PPU's dash dance game and try to imitate it. This might seem tough for someone just getting into the game, but movement is one of the most important parts of the game. Start with small sections of video and see if you can emulate the exact combination of dashing and wavedashing that you see. Make sure that your wavedashes cover the maximum amount of horizontal distance .
After this, I would highly recommend the 20XX hackpack for training alone. Here us the thread:
http://smashboards.com/threads/the-...2-action-toggles.351221/page-30#post-17037654
It has so many utilities and is amazing for self-improvement. It is used by top level players such as mango and leffen. Other people in this thread have talked about what cpu's to play to get the optimal di. Scratch that. The 20xx hackpack makes cpu's input random di and tech patterns. Cpu's will also jump out of hitstun, making you stay honest with your combos.
Make sure that you toggle color changes for hitstun and missed l cancels. Don't try to combo the cpu after they jump.
Here is a list of things you should work on(with 20xx hackpack mentioned above):
platform tech chases w/ up air
chain grabs(w/ pivots) see this thread for optimal chaingrab vs fox:
http://smashboards.com/threads/compilation-of-matchup-guides.341532/
dealing with spacy shield pressure using an ingame toggle for pressure and infinite shield(know when you can wavedash or roll out of shield)
sdi vs fox up air
Additional options(harder, takes longer to get down):
powershielding falco's lasers
hax dashing
shield drops
pivots(
https://www.youtube.com/watch?v=WuCCmymFpMU&feature=youtu.be)
Make sure you play with actual people though, so you can apply your practiced techniques. Try and get a friend over, or go to a local tournament or smashfest. Use your local facebook match to connect with your local scene.