Lemme throw in my 2 cents if thats ok =]....
..I think one of the key things to learn with Millia is reading the opponents defense. It's all about feeling your opponent. How they move around, their patterns, what they like doing, what they like doing on specific situations. The more you play Millia in actual matches, the faster you'll be able to adapt. Millia's not all training mode.
It's all about feeling out the situation. Always think ahead. Don't just throw out random mixups. Do mixups that call for the situation.
For example, you just did a knock down, and your opponent has a meter. Now lets start thinking... this guy will most likely DAA your attack on wake up. So obviously the worst mixup to do is an attack that hits low. Since he will most likely block low and then DAA. So a better mixup is an overhead. But theres still a chance for him to DAA since he might block high. So the best mixup to do in this situation is to throw them.
You can do it with..
FRC HS Tandem Top... then run up and throw...
What if the opponent has a decent wake up/overdrive move? Then you can FRC HS Tandem Top... dash back... THEN run up and throw.
No meter to FRC with? Then you can delay HS Tandem Top... then run up and throw.
So what if you just threw a Tandem Top and you're running to them and about to throw them but they jump out.. react to it, and super jump and air throw them.
And all that is just one mixup for one situation.
Her mixups are all about having backup mixups within backup mixups within backup mixups. This means if your mixup/setup gets blocked, you immediately adapt and have another mixup/block string ready to do within the next millisecond. Keep up the pressure. Don't let them breathe.
Some simple examples...
2k into 5k, into 6k... overhead gets blocked... cancel the 6k into roll then throw
or
FRC Tandem Top...into Tiger Knee Badmoon.. overhead gets blocked... opponent blocks the FRCed Tandem Top...run up to them throw..
or
HS Tandem Top on wakeup.. low hit with a 2k... gets blocked.. opponent blocks the Tandem Top.. run up to them... do 2 2ks.. then instant overhead into tiger knee badmoon.
Sometimes its even good to telegraph your mixups. . Be predictable when your opponent thinks you're going to be unpredictable. If your opponent gets hit by 2 overheads in a row, then they're gonna start blocking high the third time. So you go for a low hit. Wanna be an ass and see if this guy doesn't learn his lessson? Then do another overhead the third time. Does it get blocked? Then immediately go with the backup mixup that calls for that specific situation. You gotta have a plan A, a plan B, a plan C, etc.
Another thing is... block/bait bursts. Learn them. Know the setups for blocking/avoiding every burst situations. Millia shouldn't get hit by bursts 90% of the time... if not higher. There isn't a lot of safe situations or moves to burst against her. Millia is a character who you shouldn't carelessly bursts against. So make sure you make you drill that into your opponent's head and make them learn the hard way. I personally don't like it when there are times that I do get hit by a burst, since I know I could've avoided it. Johnny is probably IMO the best burst eater since he's usually out of range against bursts when he's comboing you, and he can punish your burst with ridiculous damage if he has meter for an FRC. There can be a disadvantage to this though. You might psyche yourself out in trying to block/ avoid bursts especially against better players, that you don't continue your combo or throw off your timing (sometimes I still do this). If you're doing a combo and yor tried to bait a burst by not continuing the combo, but the opponent didn't burst, make sure you keep up the pressure.. or go with a certain setup that calls for that situation..
For example..
2k into 5k into 6k.. opponent gets hit with the overhead... cancel 2k into FRC iron sabre then block or dash back to avoid burst... but opponent doesn't burst... run in then throw.. or another 2k into 5k into 6k or whatever mixup of your choice.
Don't get discouraged when your mixups are getting blocked. Either they're getting really lucky or they're smart. But they are not psychic. They might think they're smart by countering or avoiding your setups. But they have a disadvantage. They still can't read your mind. So its up to you to be smarter and adapt against their defense. You're the Millia player not them. So you should do the right setup for the right situation while adapting against the specific character and the specific player.
And the most important thing is dedication. Don't give up. I know a lot of players who tried to pickup Millia and have asked me for advice.. only to substitute her for a better, easier character. There's been countless times when I thought that Millia was a horrible character. Anyone who I've regularly played against know that I've said this a lot before. Her rushdown and pressure isn't as safe as Eddie, her priority isn't as high as Slayer, her pressure strings isn't as solid as Jam, doesn't deal as high damage as Robo-Ky, she can't spam the screen with projectiles, and she has the 2nd worst defense.
I've been playing Millia for so long, and I still don't think I've reached that level where I'll be completely confident and satisfied with her. If you've only started playing Millia for a couple weeks and you're already wrecking shit up with her, then most likely your opponents are not that good or at least needs to learn how to fight her. Millia has a very steep learning curve. Her combos are hard, her mixups are hard, and winning against good players with her is hard.
But I think Millia is one of the characters in the game who has the best chance of beating any player and any character (Eddie probably being the best and Millia 2nd). Because of her versatility and ability to adapt. Even against Slayer, her counter character.
All in all just play Millia smart. Millia is not an auto pilot character like Eddie. Playing auto pilot will get you killed fast especially against better players. You can't get good by just reading frame datas all day and practicing combos in training mode can only get you so far. It's all about in game experience. Don't just do the same combos over and over. Millia has tons of combos especially for specific characters. Change it up so your opponent doesn't feel the rhythm and timing of their wake up. Sometimes do long combos.. sometimes do fast ones that knock them down instantly. Play Millia swift and relentless (at least what I prefer). Get a good rhythm and feel for her. Never panic. Adapt fast.. offensively AND defensively. Always look for ways to improve yourself.
Hope that helps guys. sorry for the long post..