Legion Commander is a strong carry, single target initiator and potentially high damage dealer. Typically you want to lane her and give her farm priority, but she can also jungle.
Skills
Max Press the Attack first. Think of it as a heal on steroids and a dispel (similar to Abbadon's Aphotic Shield).
Get Two points in Overwhelming Odds for the lane presence it grants you, then max Moment of Courage.
Always get your ultimate Duel whenever you can (levels 6, 11 and 16), and try to make use of it asap to gain permanent damage.
Your combo is: Press the Attack > Blink/Shadow Blade onto enemy > Duel.
Items
Optimal item build: Power Treads into an initiation item for Duel (either Blink Dagger or Shadow Blade).
Fall-back build: Power Treads into either Armlet of Mordiggian or Drums of Endurance then an initiation item.
Good luxury items: Black King Bar (activate before you use Duel), Desolator, Mjollnir, Assault Cuirass, Heavens Halberd, Skull Basher into Abyssal Blade.
