How to level up?

http://www.steamgifts.com/about/faq

create giveaways. bundled games give small amount to your overall level, non bundled games make it go quicker.

There is also finding a potato that resembles Gaben.

Sacrifice a lamb to Gaben every full moon, hunt the great ogre in the Northern Mountains, wash yourself in the River Helk in the Forest of Dake and collect the roses from the Thorns Below. Beware the three headed griffin with steel claws and spiked taiil that is drenched in poison.