Tips to Use Sven (Dota2)

• Early on Sven has very low mana, so building mana boosting items may be a good idea.

• Drum of Endurance is a great item as it meshes well with Sven's role and play style.

• Take Stats over the two other skills instead if you want more Mana, Attack Speed and Strength to increase the bonus of God's Strength early on and to help sustain your mana for using skills. However, this is only useful very early on, as Warcry is amazing for teamfights and Great Cleave helps Sven's farming speed.

• If you prefer to initiate, get a Blink Dagger. Blink to your target and stun them with your Storm Hammer, make sure you activate God's Strength immediately or beforehand, which is more preferable as you can save more time on the casting animation and transformation time.

• Avoid leveling Great Cleave early on, as it will greatly push the lane towards the enemy tower making farming more difficult.

• As a melee carry without a blink, Sven is especially susceptible to being kited and having crowd control effects placed on him, negating his damage output. Don't skip Black King Bar to buy more damaging items, as it may result in doing no damage at all.

• Sven's unique position of being a Support and Carry at the same time, can make him a decent babysitter for a ranged carry like Weaver, Luna, or Sniper. Build arcane boots to give you and your lane partner more mana, so you can pop your Storm Hammer and Warcry more often, and focus on massing gold once your carry has had his fill, this can put you in a situation of having 4 fed carries on your team, giving your team a bigger edge on long extended games, altough it can be difficult to pull off, so use this tactic carefully. 

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