If you look at the front page of BYONDscape right now, you'll notice a series of DM tutorials written by Kunark. Some of the strongest general DM tutorials I've seen (rivaled only by the DM Guide, in my opinion), I highly recommend reading these:

Part I: http://byondscape.com/ascape.dmb/Kunark.2005-1231/
Part II: http://byondscape.com/ascape.dmb/Kunark.2005-1231.2/
Part III: http://byondscape.com/ascape.dmb/Kunark.2006-0503/