Legion Commander is a very snowbally hero that excels in catching her opponents off guard and gaining momentum to help carry her team to victory. Early game can be a little difficult, good players will understand this weakness and try to stop her from getting big in mid/late game so make sure you're keeping tabs on that Minimap. This is why I like to play Legion Commander in the jungle or safe lane to get a fast 6 without much trouble from the enemy team. Jungling in particular Press the Attack and Moment of Courage are excellent tools to help you clear camps efficiently. Once you hit 6 your Duel alone will help you push it out of laning phase and turn you into a roamer.
The main goal of playing Legion Commander is to get as many duel stacks as you can. With that bonus damage, maxing attack speed helps you shred though the enemies armor.
Power Treads are the best choice on Legion Commander as for your Overwhelming Odds already gives you a movement speed buff.
Shadow Blade is the item this build revolves around. Catching your enemies off guard and getting your bonus damage is vital.
Maelstrom good attack speed, plus the magic damage proc. What's there not to love?
Black King Bar Needed if the enemy team has a lot of disables to keep you from chopping them up.
Assault Cuirass Not only does it boost your teams armor and attack speed, but decreases the other team's armor as well.
Jungling is my personal favorite position to play Legion Commander. By using Press the Attack and Moment of Courage clearing camps is a breeze. Taking a Tango, Stout Shield, and Quelling Blade are the items I buy when starting in the jungle, if you want to spam Press the Attack or are having a bit trouble with your mana purchasing a quick Ring of Basillius is a good choice.
Without any distractions you can get a reasonably fast level 6 and then transition into ganking and getting your Shadow Blade Heroes that work well with Tresdin are Pudge, landing those long range hooks into his stun provides easy prey for your Duel. No matter who gets the kill you walk away with bonus damage and Pudge walks away with more strength. It's a win/win. Other heroes that work well with Mirana for her Moonlight Shadow, helping you get into position to quickly burst down an enemy.