Hi there! Welcome to the boards.
I'm a relatively new GM for Pathfinder as well (been running a weekly game for the last year), but I used to run 3.5 games about 6 years back as well.
Getting the Beginner's Box is a good start, it presents a stripped down version of the rules that will allow for simple adventures while you're all learning the basics.
There's a few tricks I've found helpful during the current campaign. Hopefully they'll be of some use to you.
- First up, sit down with your group and have a chat about what sort of game you're all interested in playing. There's a lot of different ways to run an RPG, so it's good to get everyone's expectations straight first. You don't want to start running what is intended to be a serious story and have players start showing up with joke characters.
- I'd suggest using the box to get a grip on the basics of the game, then start looking at transitioning over to the full game. When you do that, start with a few low level modules. The prewritten ones are a good start as they give you a ready made story so that you can concentrate on running the game. The We Be Goblins! free modules are good introductory adventures, and pretty simple to run. The Price of Immortality trilogy (Crypt of the Everflame, Masks of the Living God and The City of Golden Death) if you'd like a more serious game to learn the new rules with.
- Read, read and read some more. This goes for the rules, the characters your players make, and any adventures you plan on running. You want to have as clear a grasp on the capabilities of your players as possible, and be very familiar with the challenges you're throwing at them.
- Limit options to what you're confident you can handle easily. If you're not comfortable with some of the expanded options in the books beyond the Core Rulebook, then don't let them be used in your game until you've looked into them properly.
- Be ready to change things on the fly. There's a simple truth in all RPGs. No matter how carefully you plan a storyline, no matter how well thought out everything is, odds are it won't survive first contact with players. Don't rely on them taking one specific route, you need to be able to rework things. Whether this means providing alternative routes to the original destination, or if you just make up a whole new event on the spot is up to you. Just be ready to think fast.
- Lastly, make sure it's fun for everyone. That means you too. The GM is as much a player as the rest of the group. One of the things I make sure to do is have regular chats with the group, normally just after a session, to make sure that everyone's having fun and nobody feels like they were getting the short end of the stick in the game.
Anyway, as I said, hopefully you'll find some of this advice useful. If you ever need help, just post and the boards will normally get you plenty of answers. Whether or not they're the answers to your actual question is another matter, but hey, that's the internet for you :)
Just a heads up too, the Pathfinder Society is actually the Organised Play campaign for Pathfinder. This thread probably belongs in the advice section of the boards. I've flagged it to be moved to another location by the mods.
Anyway, have fun, and I hope the game goes well. Let us know how it goes :)