Sven is strength hero with the most damage dealing hero in dota so far. So here's how you go as rampage beast with sven:
1. Get bottle for first starting item.
2. Early game you want to get power treads and mask of madness.
3. Get crystalys and don't complate daedalus
4. in my way NEVER GET DRUM OF ENDURANCE.
5. Get blink dagger after crystalys if you think it's needed (in case enemy has sniper or some fast/ranged hero)
6. If you think enemy is doing more damage to you than your sven is doing, do get a blademail specially for troll,phantom assassin and in some cases spirit breaker.
7. Never engage yourself in teamfight as a starter of fight. Make sure your friends start the fight for you and try ganking enemies from the behind during the teamfight. It gives you pretty good chance that you'll get most of them killed. Even if it kills your team in some cases, your team owns this to sven. Because they should know sven can lead whole team to victory alone.
8. In late game try going for heart of tarrasque and any expensive situational item like MKB/Abyssal blade.

I use this lvl guide with my items..
Level up guide:
1.stun
2.cleave
3.stun
4.cleave
5.stun
6.Ulti
7.Stun
8.cleave
9.cleave
10.Warcry
11.ulti
12.Warcry
13.Warcry
14.Warcry
15.Basic attrib
16.Ulti

Important notes:
1. You must do mid with sven if enemy has pudge, any agility hero or any intelligence hero in mid(except silencer and outworld)..
2. try ganging up on enemies from the behind and use your blink dagger for this purpose.
3. in most cases fighting against A.M/escapers like storm spirit and weaver, try to initiate fight without use of storm hammer and when they are almost half of their HP or when they are trying to escape, USE STUN. this gives you much more advantage in fight than starting with the stun instead.
4. sven has a downfall....it is that sven can't do good lane against OD/Silencer in the start so you in those cases, you can lvl up according to your choice.