just clear the wave with Bladesurge and poke with you AA people back of instant when they see your PTA procc.
when you reach level 2 you can go all in when you have at least 3 stacks of ionian ferver with Flawless Duet then Bladesurge then AA til they run away and Bladesurge again to keep sticking onto them

just roam and support in river fights. maybe steal red with your jungler if possible

focus on farming and helping your team. don't get greedy cause you do damage, you are still squishy as hell so let the tank do the work. only use your Vanguard's Edge in fight and not to engage.

to take objectives it is important you use as much abilities as possible. for example taking scuttle: you go Flawless Duet>AA> Bladesurge>AA> Defiant Dance>AA> Bladesurge>AA.

in lane it's important you watch your cooldown on Flawless Duet because its your only way out if the enemy engages. play safe when it's on cooldown but dont engage right away when it's off cooldown, that way the enemy cant predict you. if he can't predict you he can't counter you.

when farming CS you mustn't use Bladesurge too much because you lose mana and make yourself vurnerable due to the dash on/behind the minion. it's way better to just AA and play safe, your AA range is the largest of the meelee champion attack ranges so use that to your advantage.

early game combo

Flawless Duet> Bladesurge>3AA's> Bladesurge
this is your main combo for the early game. when you have Tiamat and Berserker's Greaves you'll be able to kill your opponent when you have enough stacks of ionian ferver.

all in

Flawless Duet> Bladesurge>AA> Vanguard's Edge>AA> Bladesurge>AA> Defiant Dance>AA> Bladesurge>AA

this is the maximum amount of damage you can do with your abilities but is hard to master. in a teamfight you want to Bladesurge on everyone affected with Vanguard's Edge to stack ionian ferver.

Flawless Duet>AA> Bladesurge>AA> Vanguard's Edge>AA> Bladesurge>AA> Defiant Dance>AA> Bladesurge>AA

this combo does even more damage but you have to be in range to execute it, not usable for long range engages.

so in the mid lane what do you use Defiant Dance for?

defiant dance is used to block physical damage, so its most usefull when a talon or zed ults or when the enenmy bot lane engages. ectually you just need to use it when you're about to take physical damage and cannot damage the enemy.
it's also usefull to counter a zonya's hourglass due to the increased damage over charge time.