20 is fantastic for your first year, congrats!
From experience, the next batch of clients should (or have) come from referrals.
After your first year, you may actually lose several of those clients, because you will want to get rid of them. During my first year, I have learned what doesn't float well with me, for example:
Having less clients allowed me to start relationships
This turned out bad for me, because now (years later) they expect me to still have 20 minutes to spare talking with them.
GOOD + BAD = BAD
Being able to communicate with your clients may seem like a great thing at first, you will feel like a hero, the "lawn guy with a personal touch". This is going to kill you later on, but you actually need
to have this learning experience.
Being new, I allowed for my clients to negotiate.
Big mistake, as you grow these clients will become a burden - they take up all kinds of space and resources. If you can't find a way for them to pay you more, you've gotta drop them and break hearts.
Being new, I accepted every lawn
I felt successful having many lawns, however, the majority of my starter lawns were terrible. We're talking hills on top of hills, with obstacles to maneuver around every couple of feet.... Sure I got paid well, but a lot of my time was wasted, a major drop in productivity.
Lots of crap lawns = less time
less time = dead end
lots of good lawns = more time
more time = more lawns
Right now I'm extremely picky. I wont even quote most lawns, and it's one of the best changes I have ever made.
For me, I always retain approximately 77% of my previous clients every year, and I receive 37% new business every year (mostly) from referrals.
All of my clients had an optional survey on their contract, but most were too ignorant to fill it out... One of the questions was, "how did you find out about us?"
One customer wrote, "I saw you cutting grass, I walked over and said hello can you cut my grass next year, you said ok"
Forgot what we're talking about here... Off topic yet?