The most important tidbit for a new GM (sometimes referred to as Rule Zero) is: this is a GAME meant to let people have FUN. Every rule, every plot point, every character, every everything should have an aim toward the goal of having a good time with friends and fellow gamers. If your group all has that mindset, a lot of things get easier.
I highly recommend having what we call a Session Zero, where before you start telling the story and rolling dice, you have a discussion about group expectations and lay some ground rules: what kind of characters do they want to play and how will they work together? what sort of stories/encounters are you looking for (combat, social, intrigue, space combat, trading/commerce/smuggling, etc.)? Check out this thread for some good ideas: http://community.fan...-touches-paper/
Also, as has been repeated often, this game is about the narrative over the rules. The Corebook repeated notes that the rules are more like guidelines, and the GM (and the players, to some extent) should use common sense often. There's also the Rule of Cool: if it sounds awesome, find a way to make it happen, even if you have to bend things a little. Along that line, as a GM, it's often good to answer your players with a "yes, and..." or "yes, but..." instead of just nixing something.
If you have some time, consider perusing some of the below threads, where other new GMs have collected a lot of advice.
Above all, welcome to the GM club! Have fun, and if run into crazy stuff, know the community is here for you.