We're just beginning the third module, and I've been DMing for about 5 years.

1. Make sure to let the players know ahead of time that out in the wild of the Riverlands, there are creatures that are simply and literally too powerful for a party of four (and maybe even five or si PCs of their initial level. One option - the RUN option - must always be in their minds.

2. The modules themselves are done very well (as is most anything Paizo makes), but they are generic since your players literally don't have their characters inserted yet. Make sure to take any time you can to customize the campaign to the party. (This especially helps starting in the second module (Rivers Run Red), as they build and grow their Kingdom.

3. As the DM, have a good grasp on traveling rules. Remember that each hex represents 12 miles, and reference the table in the back fo the first module, as well as the overland traveling rules in the Core Rulebook. Break for rest and such when applicable, and don't forget to roll for random encounters twice for each hex. (5% chance of an encounter whenever they enter a hex, even one they've already explored, and 15% chance of an encounter for every day they spend exploring a hex.

4. This one is iffy. I normally don't care about the little details of how much food the PCs have or when they eat, hunt, and camp, but this campaign provides a perfect example for the more woodsy-type characters to shine and show how cool they are with Survival checks and stuff. If it's not too much for a newer DM, make the PCs keep track of food and water so they don't die. Starvation and getting lost in the wilderness are really fun when handled right.