I don't generally analyze myself while I play, but hopefully I self-aware enough to be of some help.
Make sure you don't Dair his shield. If you try for a fair string (which it sounds like your doing since you prefer him in the air) and he shields it, then end it with bair, which is usually prevents punishment if you're moving away from him, or just use you double jump and get away. If he's punishing your Fair before you even have time to do anything else (like with Nair or Shuttle Loop), then simply stop Fairing.
Use more Ftilt and Dtilt. I've never actually taken time to observe whether you can outrange meta's ftilt with these, but if you can't you still have fsmash, but try to use that only after you know he's commited to an action (like spamming a tilt or something)
Also, BAS should be really helpful against the type of metaknight your describing. Assuming he's not one that tornadoes a whole lot, then BAS at midrange should trip him up, maybe even force him to roll or jump.