I have just made this jump, i picked a system I had never played (but all my friends have been gaming for at least 20+ years so 3.5 to pathfinder wasn't a huge jump) but choose a scenario i thought sounded fun (skulls and shackles). The first module was a bit railroady as I didn't have the confidence to let them stray from the path, and they were nice and let me.
I am now on the second module where they have the ship and they are trampling on the module as the gloves are off, and I am having to assert myself. I set up an event and then let them run with it.
If your party has a rules lawyer listen the them unless it is really incovienient and stamp your feet and say "I AM THE DM I don't care what the book says, THIS HAPPENED" but only do this if it will increase the fun.
I count my success by the lol count, 5 good lols a night = good fun night.