Ah yes Terraforming. I have mixed feelings on it personally. One one hand its very awesome where you can make rivers and cliffs however you wanted it to. At the time I thought this was a really great idea. However, trying to do terraforming is easier said than done. When I first played this game I had no idea what I was even doing with terraforming. I was trying to make cliffs and make rivers to how I wanted it to be but, I just couldn't get it right. I find myself having to start over and terraform again but then I just screamed because I couldn't make the right paths.
Then I checked people's islands to see what they did and even watched tutorials on YouTube to find out how they did those certain things. So then I got a better understanding for how Terraforming works. I was able to make a lot open rivers, high cliffs, and of course waterfalls on my island. It was hard work and let me just say it takes a long time to do. I put in over 3,000 hours (yeah I know its crazy but that was the most time I spent in this game during the lockdown) into this game terraforming. There was a moment I was happy with how my island was but then its like I wanted to do it all over again. So then I flatten my island.
Let me just say this is the most annoying part about terraforming. It takes a very long while to do tear down a lot of cliffs and get rid of rivers on your island. Also sometimes whenever I tear down my character for some reason tries to rebuild a cliff or water, but then I wanted to tear it down. This took forever but at the end of the day it was worth it.
Overall Its one of the best features ever added to this game, but also the most tedious thing to do. Now just take your time and just make whatever you feel stands out to you. What I usually like to do is start connecting the rivers (depending on what River layout you have) and then I start working on the cliffs to find out how it can connect, so then I start to piece together where everything will go with the Bridges and inclines. Finally I use custom patterns to mark where buildings will go. Thats some tips I can give. Again just make what you feel stands out to you and take your time.