Simple enough, ideally you put together 4 Dragonmancer units from the get go. Make sure you always make Lee Sin your Dragonmancer Hero! Level up to 4 at stage 2-1.
At level 6 you want to play all low-cost Dragonmancers to make sure Lee Sin is buffed up as much as possible. Add Qiyana for a quick stun in Tempest as well as more damage for Lee. Level up to 6 at stage 3-2.