I'm another one who is doing the mowing caper. A temporary thing thanks to better half and her cancer, I needed the flexible hours.
There is some sound advice already here for sure, I know you said your not a trady but I am sure your good at something out doors.
I have been making 60 % of my money from NOT mowing, for eg:
Did an hour in the gardens for a lady the other day, she couldn't open her shed door, then I was back for 6 hours of shed repairs. The only tool I took was a battery drill.
I also take rubbish away, then sell half of it on Gumtree, charged a rich guy $160 to take away 2 of 3 x 3m garden sheds, I pulled them apart neatly, sold them on gumtree for $110 each.
Another lady I help out, I noticed the timber fence was a bit dodgy, then at a garage sale 1 day, scored a good nail gun cheap, with heaps of nails for the timber fence, so when I went back next, took it all along with me and suggested to her that I fix the fence whilst I was at it. Bit cheaky I know, but when prompted politely, she said she was not aware of it falling apart like that.
My tips
Take good weed sprays around with you, and know how well they work. Use the type where you make the dose.
Have a water blaster as well, with a long pressure hose, I do a lot of clean ups, use CT 18 truck wash as the soap, and get good results.
When your on the job, make observations of other things that may need doing and point it out, a lot of people don't notice things out doors.
Check your work before you leave. On a mowing job 1 day, Mr Franchise shows up across the raod and set a land speed record whilst there, my customer and lady over the road were talking as I was packing up, I noticed the poor job across the street and seen how disapointed the lady was. Without asking for anything from her, I draged my mower over and fixed it, now I do 3 x homes beside each other when I arrive.
All the best with it
Cheers
Dave