Flying would pretty much require a following camera perspective. First person would work, but why turn into a (hypothetical) dragon if you can not see yourself?
I really don't like First Person view in RPGs

For flight you would need controls for speed, pitch (up/down - same controls as for forward/back on the ground) and yaw (left/right); roll should be handled automatically when turning, since there isn't really a need to independently rotate about the length of the dragon. Speed usually shouldn't need to be changed during an attack, but if you never need to change pitch (ie the angle of attack) fights would get kind of boring.

For speed you could use the same button as you would use for sprint.
wasd+mouse would do the trick moving around. And imo speed should be able to change during the attack thats one of the advantages of flying get some heigth first,
then drop down at an insane speed and your enemys won't know what hit them. And aiming at a target with a constant speed is alot easier as aiming at a target that can go from very fast to slow to not moving at all.

Between attack and flight controls, I think an automatic targeting system would be handy (without frequently pausing or turn based combat, I can not think of a way to fly and attack effectively if you have to select targets yourself). The closest opponent directly in front of you could be selected (maybe add a hotkey to cycle through available targets), allowing you to simply attack or left click an alternate target.
You can still click to move (fly to a point directly above the click), and ctrl-click to target the nearest opponent to the cursor, but that bypasses flight controls, and if your enemy has ranged weapons and decent aim, always flying in a straight line to attack isn't really a great idea.
It doesn't matter if you are flying yourself or on another creature for the purposes of the combat system, you still have to control both flight and attack.

Imagine you are flying, in front of you are 10 enemys who are strong enough to survive more as one hit. Your char is a close combat fighter.
Now you don't want to finish them off one by one because else the other 9 could freely attack you.
Would you want to cycle through the targetting system to select the next enemy as you quickly fly in between and hit whoever comes close enough?
Imo it would be better to just hit and see if you hit them or not. Because auto targetting isn't effective when you are alone and fighting against a group.
And it does really matter if you are flying yourself or on another creature.
Because if you are flying yourself you couldn't really look left or right while flying somewhere,
but for example on the back of a dragon using a bow you should be able to tell the dragon fly overthere or circle around that enemy (or that group of enemys)
And use your bow to shoot them.
Offcourse if you use auto target (and the auto aim that comes with it)
it doesn't matter, but then you wouldn't really have to worry too much about the fighting since you just select a target start the attack and you fly around to keep yourself safe
(and the attack would continue untill the enemy is dead). But to me it would be like im playing as the dragon and not as the archer on its back.

There is no spoon !