Tips to Use Juggernaut (Dota2)

• Blade Fury allows the Juggernaut to deal massive amounts of damage early game, especially if you take Boots of Speed early on or have a teammate with a disable. Always try to lane with heroes such as Crystal Maiden, Lion, Venomancer and Shadow Shaman to increase your potential. If you have boots, and the enemy does not, look to be aggressive with Blade Fury.

• Blade Fury can be used as an escape mechanism due to its magic immunity. Using it alongside Healing Ward can result in escaping even the most difficult situations.

• Omnislash works best if you catch an enemy hero away from their creeps. Time it well to avoid wasting hits on creeps, and ensure your enemy doesn't have any blink or invisibility skills, as those will cause your ultimate to not affect them.

• Healing Ward is a great way to keep pushes going and heal yourself. Make sure you don't neglect it!

• Taking stats rather than Healing Ward and Blade Dance at very early levels may be a better idea. After all, stats are more useful in the early game due to your high mana costs and lack of survivability. Focusing on stats and Blade Fury up until you can get Omnislash makes you far more viable in survivability and mana management.

• Do not be fooled into thinking you are hard to kill while using Blade Fury. Enemies who have a high amount of physical damage, such as Drow Ranger or Sven, will be able to deal heavy damage to you even if you are under Blade Fury's effects. 

source:  http://dota2.gamepedia.com/Juggernaut