Be sure to switch stances often. It will enhance your attacks and grant you quick bursts of speed.
If you find yourself taking lots of damage, try using Jayce's Hammer Stance, as it grants you additional defenses.
For increased range and damage, try casting Shock Blast through the Acceleration Gate.
Jayce can attack in melee or at range. Pay attention to his stance and weapon color to know how he is going to attack.
If you see Jayce drop his Acceleration Gate, be careful, he is probably about to cast Shock Blast.
Jayce is strong in the early game. If he gains the advantage, play defensively.