Here's a few pointers on what you ought to be doing, as well as some helpful advice.
Basic Gameplay Essentials and Advice
Watch the islanders’ icons. A tree means a tree is needed; a flower means a flower is needed. The simple line diagram icons showing up or down arrows accompanied by a location marking arrow mean they want the landscape raised or lowered at that spot. A black scribble means they want to build something, but something else is in the way. Try relocating nearby trees or whatnot slightly until they are appeased.
Each island day consists of about 30 minutes. The villagers will begin to sleep close to sundown, but before the day fully ends. You may have to wake them in the mornings by lifting them out of their houses.
You can choose where you appear in the world each day by relocating the huge spike-like monument located immediately behind Doshin every morning.
Spread your trees out. You need enough green energy to cover the village-plot with fresh, green earth, but you also need space.
Mind your trees. Trees living close to the sea live much longer than isolated, land-locked trees. If your trees die off, the land they support and the buildings on that land will perish.
Recycle! When your trees turn brown, gather a bunch (six or seven) together in an area nearby but somewhat removed from your village (or otherwise greenery-deficient location). When bunched tightly together, they will immediately die off and sprout a ring of fresh, young trees, as well as a flower.
When the villagers build a monument, they need a flower to activate it. If you don't get them a flower soon enough, they will build a poor monument that won't count toward Doshin's goal. Flowers must be ‘created’ by Doshin by 'recycling' trees.
In order to get more advanced monuments, you have to 'create' new villages. If you place a male and a female on a new island, they will start a new village together. Thus, you can mix the village colors and created multicolor villages, essential for receiving the advanced mixed color monuments.
When you’re smaller, you can’t climb mountains very well. Be careful not to slip and fall, especially when in proximity to a village. You could slide into or over buildings or villagers. Subsequently, as you grow larger you must take more care when moving among the villagers, or you will trample them.
Pressing very gently on the analog stick allows you to creep along, giving any potentially squashable villagers a chance to escape harm. Thus, when in tight quarters, move very slowly and you'll not kill anyone.
Be sure to lift each house to check for magic boxes. Many houses will have boxes hidden inside, but note the symbol on the lid of the box to be sure about its contents.
Disaster prevention! When the map flashes and the sky grows dark, a disaster has occurred. Pause the game to display the map, and press Start again to view the location of the disaster.
Fires can be stopped by water, so lower the land in the path of the blaze until you strike water and the fire will disappear when it reaches the water.
Tornados (whirlwinds) can likewise be stopped by transforming into Jyashin the Hate Giant at tagging it with fireballs. Just don't get to close, or it will spin you around and send your fireballs off course, usually into the village!
To combat rainstorms, which travel steadily and sink any terrain in their path into waterlogged ponds, transform into Jyashin (the Hate Giant), stand directly below them and jump. By bumping into them with your head, you will gradually weaken and disperse them. However, you’ve got to move follow along with them, moving a bit and jumping and then repeating.
Also, earthquakes will occasionally plague your island. There is no stopping them, other than prevention. Disasters stem from a lack of green energy, so cover your island with trees and avoid leaving vast spaces devoid of greenery (even mountains).