A few things I wish someone told me when I decided to start doing the GM thing:

Do not be too ridged with your story. Roleplayers can be extremely unpredictable. If too many things "have" to happen in your story, especially as far as character interation goes, you will be sunk. This is especially true for the beginning when you don't know how all the characters are going to act. 

Have flexible plot points that don't require everyone to be there. If you can move the plot by yourself if the need arises, all the better. Though better still is if you can have events happen around the other players. Most players like the idea that their characters are important in your world. Though there are some that like alone time to develop their characters too. 

It doesn't hurt to occasionally ask how a player is doing. It's best to get an update regularly instead of just when you think something is wrong. I tend to ask all my players how they are enjoying things about once a month. Do this via Pm. You might be surprised with what they say.

Take input from everyone. You don't have to take everyone's suggestions, but if someone feels like they're being ignored they won't stick around.

You won't become an epic GM in a day. Learn and grow.