This guide is a work in progress
Generally wanted to get the skill build out with a bit of an explanation.
Having played slark over the last few weeks in dota 2 i've noticed that a lot of people get Essence Shift as early as possible and either delay dark pact or Pounce.
My reason for maxing Pounce first is, its a great innitiator/escape as well as a nuke. The starting cooldown is so long that you generally only get to use it once in a fight. By maxing it you are garuanteed that you can use it every 8 seconds - this has nettet me so many kills or enabled me to get out of sticky situations or saving a team mate so many times that its my go to skill most of the time.
An early point in DP is taken on lvl 4 because it can and will save your *** - the damage is low enough to not cause a problem with slarks low hp, but imjportant enough to dispell the nasty stuns and slows preventing you from escaping a bad situation or getting a kill with pounce.
Essence Shift is maxed after those 2 core skills because:
1) Slarks attack speed is nearly 2 seconds(1.7) meaning that 1 point in ES is enough early game(it has a cooldown of 0.4 seconds so more than enough to work on each attack), it lasts 15 seconds(you either get a kill or you dont).
Maxing essence shift is not benefitial till mid-late game because you wont have the mana or high hp to fight all the time anyway so 15 seconds/combat is more than enough early game.
Ulti taken on 6-11-16 is a no brainer. Makes for a happy healthy Slark.
Ideally you can net a kill at lvl 2 or 3 with this build and a team mate with either slow or stun - can even land it at lvl 1 with a drow with frost arrows :) simply pounce to catch, frost to keep from running and slowly burn them down.
Reason for items picked are - mana stick gives mana and can save you with a small boost of hp to either finnish the fight or get enough hp to get away, poor mans shield gives early protection vs creps mainly when going for kills. power treads is next with boots first then gloves for the added attack speed.
After that if ganking is going well in your lane i find that picking up an early urn of shadows is good for you and your team.
basically you get a bit of hp, some much needed mana regen and more importantly you can use the charges to either help your friends or finnish off people you fail to catch.
after the core items the rest is dependant on the game really
either go for basher first if things go really really well - getting it upgraded gives you 100 damage bonus and a stun.
if game goes really bad and you are facing a lot of melee heroes, you can pick the sange and turn it into the heavens halbeard - dont forget you can use that to disarm people so you wont take damage - 4.5 seconds of no damage from clinkz/drow or PA can really screw the other team just to mention a few targets :)
I usually get both items by the early late game mark