Setting up a lawn service is a great side hustle. It can be year round or seasonal.
To get started you will need to find clients and equipment. For clients, I ride through my neighborhood and look at the yards. Often times people want their yard maintained, but do not have the time or ability to do it themselves. So they are willing to pay someone else to cut the grass or rake leaves. Personally, I like to mow lawns. To be more efficient with my time, I restrict my self to within a few miles of my home.
For the equipment I prefer a push mower and a string trimmer. The push mower needs to have an adjustable mower height and a bagger. If a bagger is not available look for a mower that mulches. The string trimmer needs to be gas operated and easy to reload with line.
If you are on a tight budget look at yard sales, moving sales, Offer Up, or Craigslist. Remember trimmers and lawn mowers do not use the same gas. Mowers use regular gas while trimmers used a oil gas mix for two cycle engines. Do not forget safety glasses and gloves. A cooler for water is great idea too.