Are you new to gaming in general or just DFRPG?  Have you ever GM'd before?  What games have you played?
For DFRPG
- Do the City Creation phase and have your players make locations and NPC's!
- Always keep a list of Aspect (scene, character/NPC, City aspects)  Use them!
- Compel a lot.  It's what makes the game fun and it will get the players using their FP's more.
- Use character aspects when thinking up adventures
- Don't plan too much and let the players help guide the adventure and the story
- Be prepared:  If you do city creation, this'll be easier.  It's always good to have locations ready with a short list of aspects.  Same with NPC's.  They don't have to be fully written up - but just an outline.  This is especially important if you're not the kind of person who thinks on their feet very quickly (like me).
- When that fails, Be prepared to wing it.  

Unlike some rpg's DFRPG is a collaboration between the players and GM, so you should run the game with that in mind.
That's all pretty generic.  Do you have any specific questions?