when you are maxing heartseeker strike(E), you need to make sure you will hit enemy with this ability. thats why you have aegis of zeonia(W)->a jump with 1 sec stun. just easily jump on enemy chapion and imidiately cast heartseeker strike(E). 99% of enemies will runaway with low HP. if the enemys HP is low enough just finnish him with Spear Shot(Q). if enemy has more HP left you can use ignite if possible. Spear shot(Q) is also good for last hitting minions or kill steals :). after finnishing build you are little bit tanky so you can iniciate team fights with aegis of zeonia an heartseeker combo(W+E). in teamfights is good to jump on enemy that is not in middle of enemy team, and then cast heartseeker(E) into full enemy team. this can devastate enemies and your team wont have to deal so much dmg as regularly :)
Panteons ultimate is also good to start teamfights. after casting utlimate immidiately use aegis of zeonia and heartseeker strike(W+E) as is said higher. Ultimate is also good when deffending turret. easily jump close behind enemy pusher a this one will try to run away(into middle of grand skyfall=maximal dmg). grand skyfall is prefect to steal enemys baron or dragon. or when the gama lasts too long change warmog and atmas impaler for phantom dancer and The black cleaver. then jst wait to enemies to leave base a quickly backdoor the nexus. The win is yours :)