I would keep in mind the following:

1. Don't panic!

2. You are almost certainly doing a better job than you think you are

3. Read the rules

4. Start small, a single adventure

5. Consider using pre published material

6. Remember you job is to help the players have fun. Sometimes that might mean you have less fun, unless you get your personal kicks from happy players, which you should do!

7. You don't have a character! Don't overshadow the players with your NPCs

I would keep in mind the following:

1. Don't panic!

2. You are almost certainly doing a better job than you think you are

3. Read the rules

4. Start small, a single adventure

5. Consider using pre published material

6. Remember your job is to help the players have fun. Sometimes that might mean you have less fun, unless you get your personal kicks from happy players. Which you should do!

7. You do not have a character! Don't overshadow the players with your NPCs. Ever.