There is a way how to get lvl 20 in few hours of playing. All you have to do is just get some quest items (ones that fall out of bosses) and save your character. Then restart your game with saved character.
The boss which item tou have will die again automaticly and you will get experience. Save your character again and repeat this as many times as you want. This trick got me very powerful in 1st level . So good luck.