Being an active pillager is definitely the fastest way to grow, especially in the beginning. You’ll notice many accounts going inactive, and keep attacking them as often as possible, not more than 6 times every 24 hours though, in case they suddenly log on and report you for bashing.

Usually pillaging active player on your own island is not a good idea, it’s better for you that they grow as long as they donate frequently. An exeption to this would be players who don’t defend themselves and get looted by people from other islands frequently, it’s better that you get the resources than someone on another island does.
It’s important to have high level hideouts so that you can spy many possible targets at the same time, I usually just send one to each target and spy on their resources. If they have a lot I then spy on their military. It’s important to remember to blokade their harbour if they have war ships. Early on I usually don’t bother pillaging people with war ships, later on pretty much everyone does though. In the starting weeks of a new server you can usually just check out their military score and don’t waste spies spying on their military.

I suggest checking your island and your neighbor islands frequently so that you are the first one to notice when someones godly protection has run out. Trust me, your active neighbors will be looking for this as well, so don’t be lazy when it comes to this. It will really help you speed up things early on if you manage to plunder a few of these inactives that come out of protection.