This will be a three step guide to learning Imperius.

The W build is the easiest, with the E build the toughest.

Hopefully I can update this properly later.

Against most characters starting out you'll want to use the W Build.

Against Sgt Hammer and Vikings you'll want to use the Q Build.

The E Build really cuts through health bars, the larger the better.

In general you want to make sure your stuns to call out kills even with total strangers.

This is the most potent ability Imperius has and needs to be abused in pickup games.

Launching lingering Solarian's Fire to deal damage, slow and grant armour.
Angelic Armaments and Impervious to survive and escape situations.
Divine Rage and Sovereign Armour to provide alternate armour when Solarian's Fire's on cooldown.

You stab at your opponent after landing your solarian fire for damage and armour.
Use Angelic Armaments for extra protection before you dive, then launch swords after stun.
Reduce enemy damage and increase speed from spear.
Use Impervious to escape or attack through crowd control.

Mark opponents with W, close with Q after pressing E, then use cleaving basic attacks to deal bonus damage and receive bonus heals. In later levels he gets additional armour and shields to survive the enemy's stronger talents.