Here is my vision of Juggernaut's best role - second priority carry. I used to pick him over 1000 times and I know how weak he is in late game comparing to real hard-carry like Slark, Medusa, Spectre etc. So how many options do we have? Hardlane? Exp, but no farm and Jugger needs both. Midlane? Simply no, dont even try. Whats left? Jungle. In fact, Yurnero is one of best junglers - farming speed (crits), durability (healing ward) and escape (bladefury).
Here are basics:
Take crits at level 1 and go in spot between sideshop and weakest neutrals spawn. Take position close to the trees with "A" + left click so you stay out of sight for opponents hardlaner and once you see him walking to place ward and block spawn you will autoattack him couple times - most likely 2-3 strikes will land (possible crits) and he is gonna flee and waste his healing. That could be a good help in very early laning for your carry.
Farm weak spot twice - 0:30 and 1:00, most likely your teammates from ez lane wont need them at this moment for pull. At level 2 and 3 you take healing ward and use it right after getting 2 to spend mana, so MP-regen wont be wasted. Level 4 take stats to maximize farming speed, level 5 Bladefury as escape from ganks.
Shield and Talon are perfect for price to get first boost to damage and surviveability in jungle. Infused Raindrops provide MP-regen needed to fill your manapool in early game and protect you from ganks.
This build is oriented for gamestyle, where enemy has to die after 3-4 hits. Thats why PB are extremely useful to get short advantage in MS for delivering those hits after going out of invisability later with Shadow Blade.
First Core item for Yurnero in every situation - even if youve got Bounty Hunter / Riki / Clinkz in your team, even if the whole map is warded - doesnt matter, its still worth 2700 gold. Reason? 1. Exellent AS and damage boost to enter midgame and farm when Omnislash is on CD. 2. Increased MS for chasing. 3. Insane firsthit-damage boost, especially in combination with good luck and crit. All these bonuses are perfect to fit ambusher-gamestyle even if we forget about invisability.
From this point on you turn into riki and can start to periodically leave you lane for getting your first kills. Thats your main offensive item and you have to learn how to use it as wise as possible. First of all - manage its cooldown of 30 sec. Your first hit should be timed exactly before the expiration of SB-buff, so if your ambush fails you still can run away with bladefury & phase and stay alive until you will be able to use SB again and get this damn kill for sure.
You can also start the teamfight from another angle if you feel its about to clash. For example: go away from your team, come from behind into zone where enemys team supposed to be and search for hiding heroes such as Enigma, Magnus or Earthshaker who waits for moment to jump in. Successful Omnislash on them will most likely win this teamfight.
Point 1: Omnislash is extremely unreliable and needs a tool to be placed properly. There are 3 items to get close to the enemy without being spotted: Blink, Force Staff and Shadow Blade. Blink could be an option, but 2250 is lot of money for early game. IMO item without stats, damage and AS is a no-go for jugger, who needs to snowball with his rightclick. Silver Edge is only option I would suggest, Blink might only be better for walking-ulti-role in ultra late game, if your team got no initiator.
Point 2: Combination of Orchid and Diffusal will counter most possible ways to neutralize your ultimate. Bloodthorn (Orchid upgrade) replaces MKB to counter evasion.
Point 3: Yurnero has no steroid-passives and his skillset makes him to utility-hero or midgame dominator with snowball-potential, but very weak for ultralategame situations.
JUGGERNAUT IS NOT A CARRY