B1 In Search of the Unknown is a great starter module and a classic. I think every game needs one of these "how to" modules to teach new DMs how to design and run modules, especially dungeon modules. I would run it, if nothing else, to teach yourself about how the modules you're prepping are designed. Plus, so much of what you will need will be homebrew that the experience is worth the extra effort.
As a cautionary measure you might want to avoid Gary's earliest adventure modules like S1. He had this odd propensity to publish the highest level adventure at the same time he published a new RPG. Whether it be S1 for D&D or Necropolis for Dangerous Journeys. Great stuff certainly, but way, way out of most anyone's league when they first start the game. B1 & B2 are far better starters. Plus a lot of what has already been mentioned here.
Awesome, thanks. I'm not sure I've heard anyone sing B1's praises - maybe just because it's overshadowed by B2/T1?