More video studying, less CPU playing. If you must play, then organize your practice for efficiency. Don't try to practice 10 things at once. If you want to practice DDWDing, you have to just sit there and DD and WD in all the possible ways for 5 straight minutes. If you want to practice ledge dashing, grab the ledge in all the different ways and ledgedash until you don't mess up. After you've practiced the techniques that you wanted for that session and are about to get off, spend the last 10-15 minutes trying to incorporate them all together to see how instinctive they have become to your muscle memory. If you did the individual practices right, you should see a similar level of success in your overall practice. This is all just for playing by yourself btw (I highly recommend Name Entry Glitch with Fixed Camera Melee).
If you want to practice with CPUs, use a low level comp that won't interrupt you (I use 4 since they tend to mix up their DI pretty well) and just practice different scenarios. Neutral, comboing, and edgeguarding are the three main areas, but you can practice more specific stuff based on plat use, being on/near the ledge, using certain attacks, etc. As Falco, for example, you will want to practice low % pillar combos, but make sure you also branch out to practice combos without shine and if you find yourself doing a combo that will never work on a human, just abandon it. Other things to avoid are ONLY practicing vs. the fast fallers, never grabbing, and never playing patient. It's way too easy to get lazy and just approach over and over, but when you play a human they'll quickly realize that and you'll get owned. Imagine the CPU throwing out preemptive attacks at different timings or moving towards and away from you in different ways, and then react to that.
Most important thing is to maximize your human playing time. Go into the appropriate regional section and look for groups on FaceBook (there is a pinned thread that keeps track of all of them). It makes me happy to see so many new members trying to improve, so you should play local players who will feel the same and be eager to help you improve a lot faster than you could on your own.