If you’re looking to collect as many coins as you can in the shortest time possible, you will to make sure you have all the slots at the Roadside Shop (RSS) filled at all times. Make sure to still get XP points by completing activities, but sell everything that you can to get the most coins you can.
The RSS is typically better than truck orders and visitors to get coins. And don’t buy anything from anyone else’s stand either, unless you’re planning on reselling it for more. This way, you will be able to afford the machines mentioned in the leveling section needed at later levels.
In terms of selling things at your RSS, the price something sells for is tied to how long it takes to make. Fruit for example typically sells for a high price, and quickly, but takes a while to grow. Wheat, which grows in minutes, sells for much lower. Animal feed is happy medium between the two in terms of maximizing your time compared to return.
Make sure to slap advertising on everything you can as well. Hay Day gives you one free ad every five minutes, and gains you a ton of customers coming to your RSS. If you do this, plus sell everything you have every night, you’ll be rich in coins in no time.