I'm a self-taught aPat player, though I've picked up a few tips and tricks from these forums (I'm not stellar, but a lot of online players compliment me, so I'll take that as a reason to be confident). The most important thing to learn with aPat is the two stances and how to apply them: Dawn Haze (214) and Twilight Haze (236). If you remember Setsuka's 66B, that move's input is now either 2G 3aB or 214 3aB. I made the mistake of learning everything out of 2G which is very difficult to combo, not to mention limited, but can't be buffered, either.
By inputting any of your moves with 214 or 236, blocked attacks are much easier to punish, attacks come out faster and you can take advantage of more tech-crouch frames with the beautiful JFT (214 3a:B). I feel that JFT is aPat's backbone. However, first, try to get used to the Dawn Haze Twister input (214 3aB), and then start practicing inputting it in combos by buffering it. For example: (stun), 8A+B B, 214 3aB. This can combo without a Just Frame every time, if you time it correctly, so it's important to make this combo input feel natural. The next step is learning the JFT.
There's an entire thread dedicated to JFT (because it's that awesome) in the aPat arena, so make sure to take your time reading through that, but I would like to submit a couple tips that I've found to help me tremendously (assuming your thumb is used):
1. If you use your thumb, prepare for a mega-callous.
2. The directional input's speed doesn't matter... all that matters is how much time there is between pressing A and B.
3. Don't mash A and B as hard as you can. This greatly slows down your input. "Graze" the buttons just enough that they are definitely inputted, but your thumb keeps momentum.
4. Don't aim to stop your thumb at B. My thumb goes WAY past B - by aiming your thumb further, so to speak, you're going to move from A to B much more quickly. Just don't lose control of your controller or your ability to move your thumb quickly back to wherever it needs to move back to.
5. Try training your thumb to not make contact with A until you've reached the edge of the button closest to B. This actually causes A to input later, therefore closer time-wise to B's input. Most easily done by doing a 'swooping' motion with your thumb.
6. Don't give up after 10 minutes. aPat. Takes. Time. Oh, and patience. Don't forget that. I've heard it's important.
Other Just Frames are important: 1A is a solid low attack, especially when you're hiding behind Astaroth's giant flippin' hammer and telegraphing becomes void. So, learn 1A:A :A. If you don't see aPat's eye sparkle green or white or whatever everyone sees when the second attack starts, the third one won't come out no matter the timing. Also, the second attack must hit for the third one to come out.
Learn how to react to your counter-hits, typically with 6K or 8A+B B, while some even allow a window for 214 3B:B (another Just Frame you should learn!). aPat can dish out some srs damage so long as you react properly and time inputs correctly. 3B on Counter can be followed up with bA for 63 damage, while 3B off Counter can be followed up with JFT for 55 damage, or just Twister for 51.
Beyond this, learn which moves are dangerous and which are safe. I can't count how many times a match I'd get punished for using Twister when I first started playing this game. It was embarrassing. I'd like to post a lot more, but I'm far from being a top tier player, even with aPat as my main. I'm just at the tip of the proverbial iceberg.
Lemme know if any of this helps!
P.S. How do I post 1A

A without using

or spaces? :(