What is the best way to become DEMON lord?

Please be more specific about the type of DEMON that you're looking for. If you're looking for a human demon, the prisons are full of them. People who will literally slice and dice you just to watch the expression on your face. Perhaps you mean a mystical demon; for that, you'll have to conjure one of those yourself because only you know the specifications that you require (your best bet if you want to write about it). If you mean a virtual demon that you can conquer, you should put your question in the video gaming section.