Okay, here we go.
Don't stay above people any longer than you have to. At the beginning, I'd just run off the platform towards my opponent and fair as you fall, l-canceling at the end.
If someone's above you on the platform, short hop a nair. It's just my pet peeve, maybe, but I don't like people directly above me. Don't usmash, it's pretty slow.
Shorthop your aerials unless you're positive they're going to land, or you'll get punished. Use aerials at the last moment, it'll give more shield stun (for all intent and purpose) and it'll help you combo more since they'll have less time to recover. Don't double jump aerials and don't full jump them - the former can get you killed because you won't have a double jump for your recovery and the latter is too easy to see coming.
Dtilt instead of the fsmash when you're not sure it'll hit.
Edgeguard more aggressively. Don't be afraid to chase them off, or at least sit at the edge and dtilt.
Don't recover that high. Sweetspot the ledge from below.
Don't approach people from above, you'll almost always get outprioritized.
You're not playing very defensively, which works against a computer, but against a person, you'll have to learn to wavedash and lightshield and the like.
You're missing a lot of techs.
Don't punish with the ftilt when you can fair or nair instead, and at 0:53 you shoulda used a dair instead of a bair. The bair is pretty crappy. And again at 0:56, dair, or better yet, don't fall right onto them. And definitely don't use an aerial that high up, Yoshi can very easily jump and uair you to death.
At 1:15 you probably should've grabbed. Really, it seems like you're playing a poke war. You need to capitalize on every time you hit the opponent by comboing. Shouldn't be hard on a computer.
1:19 you don't want to be stuck in that place. People can hit you from below and if that was a person, they could dair into you and just shffl dairs at you until you're at a thousand percent. If you're going to stay there, at least shield and dthrow to jabs or something.
1:25 should've been a nair.
1:36 wasting your double jump like that at the ledge at a moderate percentage is a good way to get gimp killed.
And yeah. That's about it. Move choice, shffl'ing (and l-canceling in general), comboing, positioning, recovery, edgeguarding and wavedashing.