There are a few of ways to help your friends with their farms.
You can help fill some of the crates for their boat orders and revive trees and bushes. Players who need help on their farm normally put exclamation marks " ! " on the areas they need help with. Go into your friends bar at the bottom right of your screen and tap on the tab with the " ! " icon; here you will find friends who need help. Also, checking the Daily Dirt regularly will allow you to find more farmers in need of help… keep an eye out for the advertisers in the newspaper with the help sign next to their ads!
To help someone with their boat…
Find a yellow exclamation mark hovering near their boat and tap on the empty crate to fill an order. If you have the right amount needed to fill the crate with the required item, complete the crate and you will be rewarded with experience points and coins.
To help someone with their trees & bushes…
Find the withered trees and bushes sitting on their farm. If you see a " ! " sign next to a wiggling tree or bush, simply tap the tree or bush to revive it!
Your friends can choose to send you a thank you note, which sometimes come with a gift card too!