The basic everything goes -build. You need to lane your way to the top from early on to stack up Fresh Meat.

Your cookie-cutter will be Hamstring, which will be followed with autoattacking and chasing. In case of health problems, hit up Butcher's Brand immediately after. Initiating should happen with Ruthless Onslaught, followed with immediate Hamstring to rack up extra damage.

Ulti is Slaughterhouse because it keeps enemies from escaping your team and/or silencing casters/healers. You yourself should have no problem chasing because of Ruthless Onslaught, but usually you should not chase enemies too far with it.

Choose build #1 if you don't know what you should do
Choose build #2 if you need to kill lots of minions fast (eg. Braxis Holdout's zerglings)