Whatever control scheme works, everyone is different. =)
Look at smash corner's meta knight combo video again, it pretty much has all the normal combos Meta Knight has. As with any character you do have to do labbing yourself so you can understand the character better since there will always be times where a new situation arises and you might not see it again, so being able to adapt is just as important as knowing how to do combos. After all, if you pull the same combos off over and over again, the opponent will know what you are doing and avoid it.
Just remember what things can KO.
Forward Smash - It's very powerful and it's very safe to throw out because there is almost no end lag. Just beware of being attacked from above as it only covers the height of Meta Knight even if it covers rather far in front of him so you can't just be dumb with it.
Up Smash - Just be careful of small characters as they may airdodge through and punish since they might not get hit when on the ground. It's very easy to hit most characters in the roster with Up Smash. Not as powerful as Forward Smash or Dimensional Cape but it's still pretty strong.
Back air - You better be good at knowing the ways to turn around quickly in order to throw this out since it has decent range, lingers a bit and and is very powerful. Just be careful though, it can be a bit of a commitment with how long you'll be attacking.
Dimensional Cape - Not something you'll use as a KO move in every match, but you have to remember that it is there because there are definitely times where it's a good idea. It's also usable for recovery and positioning too, and sometimes you can use the attack instead. Just remember the move has quite a bit of endlag, and significantly more when you attack with it making it rather easily punished hard.
You already know about off-stage nair, but just remember if you want a little more knockback try to get that early hit.
Up Throw - It won't KO for a long time, but it's a rather reliable KO if you just have a very hard time KOing for way too long to the point where the opponent is getting 170% or higher and you're unable to reliably get down throw -> Up B. However, if you're on battlefield, the KO % can be much lower if you hit them on a platform, especially the top platform.
Of course this applies to all characters, but knowing your opponent is very important. Both character and player. What may work on one character may not work on another. While one way might be effective at KOing one player may not be the best at KOing another even if they are using the same character, so be sure to find the weaknesses in your opponent's playstyles, but remember they are trying to exploit your weaknesses too and adapt to fix their weaknesses in the process too. Getting good at this will help you know when to do your KO moves as they will come naturally. If you get desperate for a KO, the opponent will take advantage of that.
If you haven't already, watch some of your matches to see what you can improve upon. What mistakes did you make? If the other player was very good then think about multiple ways about how to avoid the ways they put you into bad situations. It helps more than you might think.
That's some things off the top of my head. If you haven't already, look at some Meta Knight guides. They won't tell you everything and there will be things you have to experience yourself to learn, but guides will drastically speed up how fast you pick up everything else in the game.
Also be sure to ask multiple people, everyone has different opinions and asking different people and watching different top level players will give you a more well-rounded idea of how you should play. I'm not a top level player, I just do very well against most people. Mainly because I read my opponents constantly since I don't do enough labbing to have full control of a character (4 frame short hops are my bane but I'm getting better at it). I can only give you a headstart, but you'll need to find someone else if you want the ultra specific stuff about top level play when you are ready.
