Here's what I did
I just retired again from my part time lawn business after doing what you want to do for 7 years. Here's what worked for me. I was 59 years old but age is a plus in certain customer demographics as it implies experience and knowledge in those first impression sales calls. I combined that with a professional image of uniform, written estimates, lettered trailer and promptness. Decided early on not to chase low ball clients by setting $35 minimum mowing fee. Charged hourly on cleanups (learned this one the hard way). Used post card mailers to generate sales leads in only the neighborhoods I wanted to work in. Decided anything else (yellow pages, etc.) was too expensive and non-specific as to location. You can't make money pulling a trailer across town to mow a couple of $35 lawns. After 2 years, only marketing was phone# on trailer and your customer's neighbors will start calling you. I only worked 4 days a week about 5 hours a day and averaged $45/hr gross after a couple of years. You get better and faster while the price stays the same. Best part time job I ever had.