After planting something that takes a long time to grow (for example, two hours for a tomato or two days for a potato), exit the game. Then, go to the system settings and advance the time for the amount needed for the plant to grow. Note: This may kill any fast crops if done too long.
Plow empty land to earn 1 experience point but lose 10 coins. Sell the plowed land to get the 10 coins back while keeping the experience. This can be repeated as many times as desired, but is less effective in future levels because of the low amount of experience gained.
Exit the game, then go to "Settings", then "General", then "Date And Time". Advance one day, then resume the game and check on your daily surprise. You will not always get a brain, but you will most likely get gold. The amount of gold depends on how many of your friends also have Zombie Farm.