Huskar is a carry that begins shining at level 6 and is also very strong in late game. If played right he is one of the best dps heroes ingame while getting his farm very fast because of huge ganking potential and nice jungling skills. Therefore it's very easy to get fed but u shouldn't get greedy which is a common mistake among husk players.
According to his amazing ability Berserker's Blood Huskar is most efficient and by far the best dps hero if u keep his health constantly low. There are several things to bear in mind to reach this low health level:
1. lose ur health fast, otherwise ur dps sucks
2. keep ur life level constantly low by balancing incoming dmg with Lifesteal
3. Use Magic Immunity to obtain ur Lifesteal
There are a lot of skills and items to deal with if u want to realise these 3 steps which I am goin to explain in my guide.
I prefer going mid because this will allow u to reach lvl 6 very fast and keep farm up. Try to take every lasthit and only harass if there is no lasthit or deny u could get instead. Ur aim is to farm Power Treads and send them via Animal Courier to u before lvl 6. As soon as u got ur Life Break harass ur enemy and try to pull him in a good spot for initiating. Then activate ur Inner Vitality and ult him. U will take down most heroes unless they escape, but dont be too risky with chasing. Just use Healing Salve and start ganking the other lanes.
If u did well with ganking just go for Helm of the Dominator and pwn the hell out of them. Now u are able to take out even 2-3 on ur own because most players will underestimate ur Berserker's Blood with low health. So dont run away just autoattack them and u will see. It takes some practice, but in my opinion Huskar is the only hero to take out several enemies on his own with that few items and that early in game. Despite this huge ganking potential the Lifesteal provides u with an amazing fast jungle farm. Try to take the ancients whenever u can and dont use heal to keep ur dps up while farming.
Armlet should be aimed next for. Huskar is one of the heroes that benefit most from it because u can control ur health very well with it. Since i told u sometimes it's better to start a fight with medium life this will be a great help for u. Nevertheless if u go for several heroes which have stun u have to calculate this and ur combo will be: Inner Vitality + Life Break and then Armlet. I also recommend this combo for beginners because the other strategy needs a lot of coordination.
The next item depends on the opponent team, if they have a lot of stuns and slows go for Black King Bar otherwise (if u still pwn without any problems) go on with Satanic.
When u use Black King Bar pls keep in mind that u wont get any stacks from Berserker's Blood but also wont receive dmg from Life Break. So the best thing would be to activate BkB with low life to keep the stacks up and then heal urself via Lifesteal which would be very risky so normally just activate it right after u ult in.
U should have Satanic by now which turns u into a beast. Satanic will allow u to kill large numbers of enemies even better. If u enter team fights u will mostly get stunned and nuked but with the help of Black King Bar and ur high farm u should be able to endure this a while to activate Satanic just before u die and pwn them all. If u manage to keep ur health constantly low ur dps will be ridicoulus high and u will take out enemies within seconds.
The next options are Aghanim's Scepter or Daedalus. If u want better chasing and higher dmg from Life Break (nice to take out tanks) head for Aghanim's Scepter which will allow u to Life Break several times in a team fight and prevent enemies from escaping. When u need more dps just go for Daedalus and show them what it means to face Huskar.
If u are fed like hell feel free to get a Divine Rapier but only do it if ur sure that ur team will dominate. Combine it with an Aegis of the Immortal (Roshan is pretty easy with Huskar unless u dont have Lifesteal) and it's probably a gg ;)
Urn of Shadows - get this if u dont put skill points in Inner Vitality, but dont forget to assimilate ur starting items to it (buy 2x Gauntlets of Strength instead of Belt of Strength)
Heart of Tarrasque - gives u too much health so u will be stuck at high health and also Life Break will cause to do more dmg to u than to ur opponent, so only take this if ur team needs a tank
Heaven's Halberd - good choice if the enemy team got a lot of autoattackers and also provides u with nice stats and a disarm ability
Eye of Skadi - get this if u have problems with chasing the enemy heroes, skadi is a buff placer for ranged heroes so it will stack with ur Satanic
There are a few heroes that counter Huskar very well, so it might be better not to pick him if an enemy already picked one of these heroes:
Doom Bringer - if he ults u with Doom u will be shut down completly and cant use any of ur skills or abilities. Most the time u will be focused before u can do anything so let ur team know to silence him or whateva
Necrolyte - a good timed Reaper's Scythe will be devastating for u, just because low life is ur best condition
Also beware of any high nuke like Laguna Blade from Lina and Finger of Death from Lion
Most of u will ask wtf why isnt he using Burning Spear, but the reason is quiet simple. Just after ur first gank u go for Morbid Mask which makes Burning Spear useless, since u can only use one orb effect. Although Burning Spear deals amazing dmg early game u will profite more from Lifesteal. Because ur most effective with low hp, u would simply die without Lifesteal. So there's no chance to take out this bunch of enemies while they think ur an easy kill :P The only use of Burning Spears is to prevent u from Lifesteal which might be good to farm quicker (lower hp more stacks from Berserker's Blood). Grab a point in Burning Spear at lvl 12 if ur interested in this.
Always be aware of how much crowd control the enemy team has, for example a Doom Bringers Doom will shut u down in most cases, so u can calculate how much to risk and how aggressive to play.
Ur tools to lose health fast and on the other hand keep it on a constantly low lvl are:
Inner Vitality, Armlet, Satanic, Life Break and Black King Bar. It's all about coordinating and adapting those tools to what the opponent team has to master this Secret Warrior. Use ur skills wisely and be capable of teamwork to spend a great time with this hero. I wish u good luck and hope that this guide helped u!
This Guide is still under construction, but feel free to give me any advice u have :D