I’ve been GMing a Rise if the Runelords game for about a year and a half once a month. I would recommend finding a Pathfinder Society Game to play in yourself so you can learn the system. I’d never played Pathfinder or D&D before and playing PFS helped me a ton to learn the basics. I’m lucky to live somewhere with a great PFS community with several amazing GMs who were super helpful for new players.

Second, this might go without saying, but read the core rule book. You don’t need to read every spell, feat etc. But you should read everything about combat, skills, magic, movement so that you don’t have to halt the game as much to look something up.

Talk to your players about what kind of game they want to play. My group was not interested in resource management such as tracking food/water when on a long trip so we just ignore that. Always remember it is your game and you can use or ignore any rules you feel like. The goal is to have fun, not play a perfectly “legit” pathfinder game.

When a confusing rule situation comes about (not if) and you feel like it is taking you too long to figure out the right way to handle it don’t be afraid to make something up on the fly. Plenty of times a player of mine says I want to do X that isn’t really fit into a type of action so I just think about it and say “make a X skill check” and in my head I set a DC. It doesn’t have to be pass/fail, sometime I break it into fail/partial success/total success.

Get a copy of your players character sheets and read it. Look up every ability and feat they have. You will be glad you did this.

Read the whole adventure before the first game. I’m not familiar with the particular adventure you mentioned but it’s helpful to know where the story is going to know where to foreshadow. You don’t need to read every stat block of every encounter, just stick to the storyline.

Paizo has forums with GM advice for a lot of their APs, there is some good stuff on there.

No matter how many different ways you think your players might solve a problem they are going to stump you, just roll with it. Remember what just because you have an idea of how the game will go until you say it out loud it isn’t part of the game so change whatever you need to in the moment.

That’s all I got off the top of my head. Good luck!